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Page No 299:
Question 1:
To study the dependence of current (I) on the potential difference (V) across a resistor, the correct way of connecting the ammeter and voltmeter in the circuit is:
(1) ammeter and voltmeter both are connected in series
(2) ammeter is connected in parallel and voltmeter in series
(3) ammeter is connected in series and voltmeter in parallel
(4) ammeter and voltmeter both are connected in parallel
Answer:
In any circuit, the ammeter should be connected in series and the voltmeter should be connected in parallel.
An ammeter is a low impedance device, it should be connected in series so that all of the current passes through it and the actual current flowing in the circuit can be measured. While a voltmeter is a high impedance device, it should be connected in parallel so that a zero or minimum amount of current flows through it and the actual voltage drop across the component can be measured.
Hence, the correct answer is option 3.
Page No 299:
Question 2:
The following four circuits have been made for studying the dependence of current on the potential difference across a resistor.
The correct circuit is :
(1) A
(2) B
(3) C
(4) D
Answer:
To study the dependence of current on the potential difference across a resistor, the ammeter is connected in series and the voltmeter is connected in parallel. As the current moves from higher potential to lower potential, so the polarities of both ammeter and voltmeter are set according to the direction of flow of current.
Out of all the given circuits, only circuit 'A' is correct because ammeter and voltmeter both are connected properly with the correct polarities.
Hence, the correct answer is option 1.
Page No 299:
Question 3:
To study the dependence of current (I) on the potential difference (V) across a resistor, the following observations were made by four students A, B, C and D.
| Student | Reading No. 1 | Reading No. 2 | Reading No. 3 |
| A | V = 0.5 V I = 0.1 A |
V = 1.0 V I = 0.2 A |
V = 1.5 V I = 0.3 A |
| B | V = 0.8 V I = 0.4 A |
V = 1.6 V I = 0.8 A |
V = 2.4 V I = 1.2 A |
| C | V = 1.0 V I = 0.5 A |
V = 1.2 V I = 1.4 A |
V = 1.4 V I = 1.0 A |
| D | V = 2.4 V I = 0.8 A |
V = 2.7 V I = 0.9 A |
V = 3.0 V I = 1.0 A |
The teacher found that one of the students has made wrong observations. The student who made the mistake is:
(1) A
(2) B
(3) C
(4) D
Answer:
According to Ohm's Law, (Where 'R' is the constant and is given by resistance of the circuit)
While observing the current-voltage relationship across a resistor, all of the readings must follow this law. That means Voltage and current ratio should be a constant value in every case.
All of the readings taken by students A, B and D give the same value of the voltage-current ratio, but the observations made by student C don't. All the three readings observed by student C give a different value of the voltage-current ratio (resistance of the circuit), which is not possible. So, student C has made wrong observations.
Hence, the correct answer is option 3.
Page No 300:
Question 4:
Graphs plotted by four students A, B, C and D for the experiment "To study the dependence of current (I) on the potential difference (V) across a resistor" are shown below:
The correct V-I graph is
(1) A
(2) B
(3) C
(4) D
Answer:
Ohm's Law gives us the dependence of current on the potential difference across a resistor. i.e. . From the given expression, we can say that the graph between I and V is a straight line passing through the origin.
Hence, the correct answer is option 2.
Page No 300:
Question 5:
The following' precautions' were listed by a student in the experiment on study of 'Dependence of current on potential difference'.
(A) Use copper wires as thin as possible for making connections.
(B) All the connections should be kept tight.
(C) The positive and negative terminals of the voltmeter and the ammeter should be correctly connected.
(D) The 'zero error' in the ammeter and the voltmeter should be noted and taken into consideration while recording the measurements.
(E) The 'key' in the circuit, once plugged in, should not be taken out till all the observations have been completed.
The 'precautions' that need to be corrected and revised are:
(1) (A), (C) and (E)
(2) (C) and (E)
(3) (B) and (E)
(4) (A) and (E)
Answer:
The resistance of a wire is inversely proportional to the area of the cross section of the wire. If a thin copper wire will be used in the experiment then it's resistance would be high, which will generate a lot of heat during the experiment and due to that, observations may vary in the experiment and the student may not get the desired results. so, statement A should be revised and corrected.
Also, if the 'Key' will be kept plugged in for a very long time then there will be some heat generations and due to that, the student may not get the desired results. so, statement E should also be revised and corrected.
Hence, the correct answer is option 4.
Page No 300:
Question 6:
An ammeter has 20 divisions between 0 mark and 2 A mark on its scale. The least count of this ammeter is:
(A) 0.01 A
(2) 0.02 A
(3) 0.1 A
(4) 0.2 A
Answer:
The least count of any device is given by the value measured by one single division on the scale of the device.
Total number of divisions on the scale of the given ammeter = 20
least count =
Hence, the correct answer is option 3.
Page No 300:
Question 7:
A student finds that there are 20 divisions between the 0 mark and 1 V mark of a voltmeter. What is the least count of this voltmeter?
(1) 0.50 V
(2) 0.02 V
(3) 0.2 V
(4) 0.05 V
Answer:
The least count of any device is given by the value measured by one single division on the scale of the device.
Total number of divisions on the scale of given voltmeter = 20
least count =
Hence, the correct answer is option 4.
Page No 300:
Question 8:
Which of the following instruments does not have plus (+) or minus (–) sign marked on it while representing in a circuit diagram?
(1) Rheostat
(2) Voltmeter
(3) Ammeter
(4) Cell
Answer:
A rheostat is a variable resistor and for a resistor, either terminal can be connected to either side of the circuit. That's why a rheostat does not have a positive or negative sign marked on it while representing in a circuit diagram.
Hence, the correct answer is option 1.
Page No 300:
Question 9:
To study the dependence of current (I) on the potential difference (V) across a resistor R, two students used the two setups shown in Figures A and B respectively. They kept the contact point J in four different positions, marked (a), (b), (c) and (d) in the two figures.
For the two students, the ammeter and voltmeter readings will be maximum when the contact J is in the position:
(1) (d) in both the setups
(2) (a) in both the setups
(3) (d) in setup A and (a) in setup B
(4) (a) in setup A and (d) in setup B
Answer:
The ammeter and voltmeter readings would be maximum when the current in the circuit would be maximum.
In set up A, contact 'J' should be connected to point 'd' as it will give the maximum value of applied voltage, hence the maximum current in the circuit. In set up B, the contact 'J' should be at the point 'a', as it would minimize the net resistance of the circuit and due to that current flow will be maximum.
Hence, the correct answer is option 3.
Page No 301:
Question 10:
In the circuit given below, the instrument B reads 0.93 and the instrument A reads 1.80 in their respective SI units.
The value of the unknown resistor will be:
(1) 0.51 Ω
(2) 1.63 Ω
(3) 1.93 Ω
(4) 19.3 Ω
Answer:
The instrument B is an ammeter as it is connected in series and instrument B is a voltmeter as it is connected in parallel in the circuit.
Current in the circuit = Value given by instrument B = 0.93 A
Voltage across the unknown resistor = Value given by instrument A = 1.80 V
According to Ohm's law, V =IR
Or
Hence, the correct answer is option 3.
Page No 301:
Question 11:
Four identical cells of emf 1.5 V each were connected in four different ways as shown below:
The potential difference between the points X and Y would be equal to 6.0 V in case/cases:
(1) A and B
(2) A and C
(3) A and D
(4) A only
Answer:
The potential difference between the points X and Y would be exactly 6.0 V, only if all the cells would be connected to each other in the same polarity. We can see this only in set A and C.
Hence, the correct answer is option 2.
Page No 301:
Question 12:
The scale of an ammeter is shown below:
The least count of this ammeter is :
(1) 0.05 A
(2) 0.5 A
(3) 0.1 A
(4) 1 A
Answer:
The least count of any device is given by the value measured by one single division on the scale of the device.
Total number of divisions on the scale = 30
Least count =
Hence, the correct answer is option 3.
Page No 301:
Question 13:
The least count of the voltmeter shown below is:
(1) 0.1 V
(2) 0.01 V
(3) 0.02 V
(4) 0.2 V
Answer:
The least count of any device is given by the value measured by one single division on the scale of the device.
Total number of divisions on the scale = 15
Least count =
Hence, the correct answer is option 4.
Page No 301:
Question 14:
Consider the following circuits:
On plugging the key, the voltmeter/ammeter is likely to be damaged:
(1) in circuit A
(2) in circuit B
(3) in circuit C
(4) in circuit D
Answer:
An ammeter is a low impedance device while a voltmeter is a high impedance device.
In circuit A, there is only a high impedance voltmeter connected in series, so a very low amount of current will flow in the circuit which will not damage the device. In circuits B and D, there will not be any damages too because of the presence of high impedance voltmeter connected in series, which will lower the amount of current flowing in the circuit. But, in circuit C, a low impedance ammeter is connected directly to the battery, hence a large amount of current will flow through the ammeter. So, it is likely to be damaged.
Hence, the correct answer is option 3.
Page No 301:
Question 15:
The rest positions of the needles in a Milliammeter and Voltmeter when not being used in a circuit are as shown in the figure. The 'zero error' and 'least count' of these two instruments are:
(1) (+ 4 mA, – 0.2 V) and (1 mA , 0.1 V) respectively
(2) (+ 4 mA, – 0.2 V) and (2 mA , 0.2 V) respectively
(3) (– 4 mA, + 0.2 V) and (2 mA, 0.2 V) respectively
(4) (– 4 mA, + 0.2 V) and (2 mA, 0.1 V) respectively
Answer:
Total number of divisions on the milliammeter scale = 5
maximum value marked = 10 mA
Least count =
Total number of divisions on the voltmeter scale = 10
maximum value marked = 1 V
Least count =
On the milliammeter scale, zero error =
On the voltmeter scale, zero error =
Hence, the correct answer is option 4.
Page No 302:
Question 16:
A student has to connect 4 cells of 2 V each to form a battery of voltage 8 V. The correct way of connecting these cells is shown in the figure:
(1) A
(2) B
(3) C
(4) D
Answer:
In order to get a voltage of 8 V from 4 cells of 2 V each, the student needs to connect all of them in the same polarity. Only combination A consists of all the cells connected with each other in the same polarity.
Hence, the correct answer is option 1.
Page No 302:
Question 17:
To study the dependence of current (I) on the potential difference (V) across a resistor, two students used the two set ups shown in figs (A) and (B) respectively. They kept the contact J in four different positions, marked (a), (b), (c), (d) in the two figures.
For the two students, their Ammeter and Voltmeter readings will be minimum when the contact J is in the position:
(1) (a) in both the set ups
(2) (d) in both the set ups
(3) (d) in set up (A) and (a) in set up (B)
(4) (a) in set up (A) and (d) in set up (B)
Answer:
Ammeter and voltmeter readings will be minimum if the current in the circuit is minimum.
In circuit A, the contact 'J' should be connected at point 'a', so that circuit gets the least power supply which will minimize the current flow in the circuit. In circuit B, the contact 'J' should be connected at point 'd', so that the circuit can have the highest resistance which will minimize the current flow in the circuit.
Hence, the correct answer is option 4.
Page No 302:
Question 18:
In the circuits A, B, C and D, with switch S open, the lamps Q and R would light up but not lamp P in:
(1) circuit A
(2) circuit B
(3) circuit C
(4) circuit D
Answer:
Out of all the given circuits, only in circuit B, the lamp P will not light up while the lamps Q and R would light up with switch S open. Because there is no current flowing in the wire containing lamp P due to an incomplete circuit, so it will not light up. Whereas, both other lamps in circuit B will light up with the switch S open because the circuit containing lamps Q and R is complete .
Hence, the correct answer is option 2.
Page No 302:
Question 19:
The rest positions of the needles in a milliammeter and voltmeter not in use are as shown in Fig. A. When a student uses these in his experiment, the readings of the needles are in the positions shown in Fig. B. The corrected values of current and voltage in the experiment are
(1) 42 mA and 3.2 V
(2) 42 mA and 4.0 V
(3) 34 mA and 3.2 V
(4) 34 mA and 4.0 V
Answer:
Number of divisions on the scale of milliammeter = 5
Least count of the milliammeter
Zero error
Reading on the main scale = 38 mA
Correct reading = Main reading Zero error = 38 mA ( 4 mA) = 42 mA
Number of divisions on the voltmeter scale = 5
Least count of the Voltmeter =
Zero error = + 0.4 V
Reading on the main scale = 3.6 V
Correct reading = Main reading Zero error = 3.6 V (+ 0.4 V) = 3.2 V
Hence, the correct answer is option 4.
Page No 303:
Question 20:
The current flowing through a resistor connected in an electric circuit and the potential difference applied across its ends are shown in the figures below:
The value of the resistance of the resistor is :
(1) 10 Ω
(2) 15 Ω
(3) 20 Ω
(4) 25 Ω
Answer:
Least count of milliammeter scale =
Value of current = 920 mA = 180 mA
Least count on voltmeter scale =
Value of voltage applied = 90.2 V = 1.8 V
According to Ohm's law,
Hence the correct answer is Option 1.
Page No 303:
Question 21:
Consider the following circuit diagrams drawn by four students:
The correct circuit diagram for studying the dependence of current on the potential difference across the resistor is:
(1) A
(2) B
(3) C
(D) 4
Answer:
An ammeter is always placed in series while the voltmeter is always connected in parallel to other electrical components in any circuit. Circuit B and D are totally wrong because of the positioning of voltmeter and ammeter. In circuit C, voltmeter and ammeter are connected at the right positions but the polarity of the voltmeter is wrong, hence circuit C is also wrong. In circuit A, both the voltmeter and ammeter are connected with the right polarities and at right positions.
Hence the correct answer is Option 1.
Page No 303:
Question 22:
The scale of an ammeter is shown below:
The least count of this ammeter is :
(1) 0.1 A
(2) 0.01 A
(3) 0.02 A
(4) 0.2 A
Answer:
Least count of any scale is the value measured by a single division on it.
Total number of division on the given scale = 30
The maximum value that can be measured = 6 A
Least count =
Hence the correct answer is option 4.
Page No 303:
Question 23:
The figure below shows the scale of a voltmeter.
The least count of this voltmeter is :
(1) 1 V
(2) 0.5 V
(3) 5 V
(4) 0.05 V
Answer:
Least count of any scale is the value measured by a single division on it.
Total number of division on the given scale = 30
The maximum value that can be measured = 1.5 V
Least count =
Hence the correct answer is option 4.
Page No 304:
Question 24:
A student used the set up given here to study the dependence of current (I) on the potential difference (V) across a resistor.
He kept the contact C in four different positions marked as P, Q, R and S in the figure. On calculating the values of the ratio for his four readings, he would find that the value of this ratio :
(1) for contact at point P is of that for contact at point S.
(2) for contact at point Q is of that for contact at point S.
(3) for contact at point R is of that for contact at point S.
(4) is the same for all the four readings
Answer:
According to Ohm's law, (Where R is a constant and known as the resistance of the circuit)
As the resistance in the circuit is fixed, hence on changing the applied voltage, current in the circuit will also change and the ratio of voltage and current will remain the same for all the four readings. i.e. equal to the resistance of the circuit.
Hence the correct answer is option 4.
Page No 304:
Question 25:
You are given the following four voltmeters to study the dependence of current (I) on the potential difference (V) across a resistor.
Which one of the above voltmeters would you prefer to use in the circuit to begin your experiment?
(1) A
(2) B
(3) C
(4) D
Answer:
If the pointer of the scale does not coincide with the zero of the scale, it is called zero error. Before using any voltmeter, we should check for any zero errors in the voltmeter. For experiments, we should always use a zero-error free voltmeter to get accurate measurements. Out of all given voltmeters only D has its pointer coinciding with the zero of the scale, so it should be used for experiments purposes.
Hence the correct answer is option 4.
Page No 304:
Question 26:
A student arranged an electric circuit as shown alongside:
He would observe:
(1) no reading in either the ammeter or the voltmeter
(2) no reading in the voltmeter but a reading in the ammeter
(3) no reading in the ammeter but a reading in the voltmeter
(4) readings in both the ammeter and the voltmeter
Answer:
As the ammeter is connected in series with right polarity to the battery so ammeter will give the required reading but the voltmeter is not properly connected to the resistor, as the switch to the negative terminal of the voltmeter is open. because the voltmeter is not connected across both ends of the resistor, that's why it won't be able to measure the potential difference or voltage drop across the resistor. So the voltmeter will show no reading.
Hence the correct option is Option 2.
Page No 304:
Question 27:
Four students recorded the readings of the current by observing the position of the pointer on the ammeter scale given below:
If there is no zero error, the correct reading of the current is :
(1) 2.3 A
(2) 5 A
(3) 2.0 A
(4) 2.05 A
Answer:
As there is no zero error in the scale hence the scale reading will the actual reading.
Total number divisions on the scale = 30
The maximum value that can be measured = 3 A
Least count of the scale = 0.1 A
The correct reading of the scale =
Hence the correct answer is option 1.
Page No 304:
Question 28:
The least count of the ammeter shown below is :
(1) 0.05 A
(2) 0.5 A
(3) 0.1 A
(4) 1 A
Answer:
Least count of any scale is the value measured by a single division on it.
Total number of divisions on the scale = 30
The maximum value that can be measured = 1.5 A
Least count =
Hence the correct answer is option 1.
Page No 305:
Question 29:
Four students measured the reading by observing the position of pointer on the ammeter scale as shown below:
Assuming that the ammeter has no zero error, the correct reading is :
(1) 1.25 A
(2) 1.30 A
(3) 1.15 A
(4) 1.1 A
Answer:
Total number of divisions on the scale = 30
The maximum value that can be measured = 1.5 A
Least count =
Ad there is no zero error, so the Correct reading of the scale =
Hence the correct option is Option 3.
Page No 305:
Question 30:
Four students recorded the readings of the potential difference by observing the position of the pointer of an ideal voltmeter as shown below:
(1) 2.5 V
(2) 2.0 V
(3) 2.2 V
(4) 2.4 V
Answer:
Total number of divisions on the scale = 15
The maximum value that can be measured = 3 V
Least count =
As there is no zero error, so the correct reading of the scale =
Hence, the correct answer is option 3.
Page No 305:
Question 31:
In an experiment to find the equivalent resistance of two resistors connected is series, a student used the circuit shown:
This circuit will give :
(1) correct reading for voltage V but incorrect reading for current I
(2) correct reading for current I but incorrect reading for voltage V
(3) correct reading for both voltage V and current I
(4) Incorrect readings for both current I and voltage V
Answer:
An ammeter is a low impedance device and a voltmeter is a high impedance device. In the given circuit the voltmeter is connected in parallel with the ammeter, so the maximum current will pass through the ammeter, that's why the ammeter will give the true reading. The voltmeter is not connected in parallel with the resistors, hence it will not show the actual voltage drop in the circuit, so it will show the incorrect reading.
Hence, the correct answer is option 2.
Page No 305:
Question 32:
A student sets up an electric circuit shown here for finding the equivalent resistance of two resistors in series:
In this circuit, the:
(1) resistors have been connected correctly but the voltmeter has been wrongly connected
(2) resistors have been connected correctly but the ammeter has been wrongly connected
(3) resistors, as well as the voltmeter, have been wrongly connected
(4) resistors, as well as the ammeter, have been wrongly connected
Answer:
To measure the equivalent resistance of the circuit, voltmeter needs to be connected in parallel across the outer ends of resistors connected in series. In the given circuit both the resistors are connected in series with the ammeter but the voltmeter is connected across the ends of only one resistor instead of both resistors. So, resistors have been connected correctly but the voltmeter has been wrongly connected.
Hence, the correct answer is option 1.
Page No 306:
Question 33:
A student while performing the experiment to find the resultant resistance of two resistors connected in series observed the ammeter pointer at position P when the key is 'off' and the same pointer at position Q when the key is 'on'.
The correct reading of ammeter is:
(1) 0.2 A
(2) 2.5 A
(3) 2.3 A
(4) 2.7 A
Answer:
Least count of the given scale = 0.1 A
Main scale reading
Zero error =
True reading of the ammeter = Main scale reading - Zero error = 2.5 A 0.2 A = 2.3 A
Hence, the correct answer is option 3.
Page No 306:
Question 34:
While performing an experiment to determine the equivalent resistance of two resistors connected in parallel, a student observes the pointer of voltmeter at position X when the key is 'off' and the same pointer at position Y when the key is 'on'.
The correct voltmeter reading is :
(1) 0.2 V
(2) 2 V
(3) 2.2 V
(4) 1.8 V
Answer:
Total number of divisions on the main scale of the voltmeter = 30
Least count of the given scale
Main scale reading
Zero error =
True reading of the ammeter = Main scale reading - Zero error = 2.0 V 0.2 V = 1.8 V
Hence, the correct answer is option 4.
Page No 306:
Question 35:
Choose the appropriate set of apparatus for performing the experiment to determine the equivalent resistance of two resistors when connected in series:
(1) Voltmeter, Ammeter, Two resistors, Key, Battery
(2) Ammeter, Two resistors, Key, Connecting wires, Rheostat, Battery
(3) Key, Rheostat, Voltmeter, Two resistors, Battery, Connecting wires
(4) Battery, Ammeter, Connecting wires, Rheostat, Voltmeter, Two resistors, Key
Answer:
For performing the experiment to determine the equivalent resistance of two resistors when connected in series, one would need Ammeter to measure the current, Voltmeter to measure the voltage drop across the resistors, connecting wire to make the connections, a battery to give power supply to the whole circuit, two resistors, a key to make the circuit open or close and a rheostat to control the amount of current flowing in the circuit by controlling the variable resistance in the circuit.
Hence, the correct answer is option 4.
Page No 306:
Question 36:
In the experiment on finding the equivalent resistance of two resistors connected in series, three students connected the ammeter in their circuits in the three ways X, Y and Z shown here.
Assuming their ammeters to be ideal, the ammeters have been correctly connected in
(1) cases X and Y only
(2) cases Y and Z only
(3) cases Z and X only
(4) all the three cases
Answer:
An ideal ammeter has negligible or zero resistance, hence it measures the actual current flowing in the circuit. It can be connected anywhere in the circuit in series with the battery and the resistance of the circuit given that current should enter into it from the positive terminal and leave from the negative terminal. The ammeter is not connected with appropriate polarity in circuit Z. In circuit Z, the polarity of the ammeter is wrong. So in circuit X and Y, the ammeters have been correctly connected.
Hence, the correct answer is option 1.
Page No 306:
Question 37:
In the experiment on finding the equivalent resistance of two resistors, connected in parallel, three students connected the voltmeter in their circuits, in the three ways X, Y and Z shown here.
The voltmeter has been correctly connected in
(1) cases X and Y only
(2) cases Y and Z only
(3) cases Z and X only
(4) all the three cases
Answer:
To measure the equivalent resistance between the two resistors, the voltmeter should be connected in parallel with the resistors and the ammeter should be connected in the series, and the current should be entering from the positive terminal and leaving from the negative terminal of the ammeter and the polarity of the voltmeter should also be in accordance with the polarity of the resistors.
As in all three given circuits voltmeter is properly placed. Hence the Correct answer is Option 4.
Page No 307:
Question 38:
The only correct statement for the following electric circuit is:
(1) The Voltmeter has been correctly connected in the circuit
(2) The Ammeter has been correctly connected in the circuit
(3) The Resistors R1 and R2 have been correctly connected in series
(4) The Resistors R1 and R2 have been correctly connected in parallel
Answer:
Both the ammeter and the voltmeter are connected with the wrong polarity in the circuit, and as both ends of the resistances are in contact hence they are connected in parallel.
Hence, the correct answer is option 4.
Page No 307:
Question 39:
The only correct statement for the two circuits (X) and (Y) shown below is :
(1) The resistors R1 and R2 have been connected in series in both the circuits
(2) The resistors R1 and R2 have been connected in parallel in both the circuits
(3) In the circuit (X) the resistors have been connected in parallel whereas these are connected in series in circuit (Y)
(4) In the circuit (X) the resistors R1 and R2 are connected in series while these are connected in parallel in circuit (Y)
Answer:
As both the ends of the resistances are connected in circuit X, so they are connected in parallel in circuit X, but they are connected in series in circuit Y, as the only one end is in contact with each other.
Hence, the correct answer is option 3.
Page No 307:
Question 40:
For three circuits, shown here
the same two resistors R1 and R2 have been connected in parallel in all the circuits but the voltmeter and the ammeter have been connected in three different positions. The relation between the three voltmeter and ammeter readings would be :
(1) V1 = V2 = V3 and I1 = I2 = I3
(2) V1 ≠ V2 ≠ V3 and I1 = I2 = I3
(3) V1 = V2 = V3 and I1 ≠ I2 ≠ I3
(4) V1 ≠ V2 ≠ V3 and I1 ≠ I2 ≠ I3
Answer:
In all the three circuit voltmeter is always connected in parallel with all the resistors, hence it will measure the same voltage each time. So, V1 = V2 = V3
In the first circuit, the ammeter is connected in series with resistance R1, and in the second circuit, the ammeter is connected in series with resistance R2, and in the third circuit, the ammeter is connected in series with the parallel combination of the resistances. As all the cases are different, each time ammeter will measure different values of current. So, I1I2I3.
Hence, the correct answer is option 3.
Page No 307:
Question 41:
Two students (A) and (B) connect their two given resistors R1 and R2 in the manners shown below :
Student (A) connects the terminals marked (b1) and (c1) while student (B) connects the terminals marked (d2) and (c2) in their respective circuits at the points marked X and Y.
Which one of the following is correct in relation to the above arrangements?
(1) both the students will determine the equivalent resistance of the series combination of the two resistors.
(2) both the students will determine the equivalent resistance of the parallel combination of the two resistors
(3) student (A) will determine the equivalent resistance of the series combination while student (B) will determine the equivalent resistance of the parallel combination of the two resistors.
(4) student (A) will determine the equivalent resistance of the parallel combination while student (B) will determine the equivalent resistance of the series combination of the two resistors.
Answer:
In combination made by student A, only one end of the resistors are in contact so they are connected in series. But, in the combination made by student B, both the ends of both the resistances are connected together, so they are connected in parallel.
When both the combinations are connected across the ends X and Y of the circuit, student A will find the equivalent resistance of the series combination, while the student will find the equivalent resistance of parallel combination.
Hence, the correct answer is option 3.
Page No 308:
Question 42:
Three students (A), (B) and (C) connect their two given resistors R1 and R2 in the manners shown below:
They connect the terminals marked X and Y above to the terminals marked X and Y in the circuit given below:
They record the ammeter reading (I) for different positions of the rheostat and the corresponding Voltmeter readings (V).
The average value of the ratio V/I in their observations would be minimum for :
(1) students (A) and (B) only
(2) students (B) and (C) only
(3) students (C) and (A) only
(4) student (A) only
Answer:
According to Ohm's law, we can say that the ratio, .
The resistors in combination made by student A are connected in parallel, while the resistors in combinations made by students B and C are connected in series. So, the total resistance between point X and Y will be minimum when the resistors are in parallel. That's why the voltage and current ratio would be minimum for student A only.
Hence, the correct answer is option 4.
Page No 308:
Question 43:
Students A and B connect the two resistors R1 and R2 given to them in the manners shown below:
and then insert them at X and Y into the measuring circuit shown below:
We can then say that
(1) both the students will determine the equivalent resistance of the series combination of R1 and R2
(2) both the students will determine the equivalent resistance of the parallel combination of R1 and R2
(3) student A will determine the equivalent resistance of the series combination while student B will determine the equivalent resistance of the parallel combination of R1 and R2
(4) student A will determine the equivalent resistance of the parallel combination while student B will determine the equivalent resistance of the series combination of R1 and R2
Answer:
In combination A, only one end of the resistors are in contact with each other, so they are in series, and in the combination B, both ends of the resistors are in contact, so they are in parallel connection. So, student A will determine the equivalent resistance of the series combination while student B will determine the equivalent resistance of the parallel combination of R1 and R2.
Hence, the correct answer is option 3.
Page No 308:
Question 44:
A student carries out the experiment for studying the dependence of current (I) flowing through a resistor system of R1 and R2 on the potential difference (V) applied to it by connecting the resistor system to points X and Y of the measuring circuit as shown:
The average value of the ratio V/I, of his observations, would then be equal
(1) only in cases A and B
(2) only in cases B and C
(3) only in cases C and A
(4) all the three cases
Answer:
Both the resistances are connected in series in combination A, as their only one end is in contact with each other. But, the resistances in combinations B and C are connected in parallel as both the ends of resistances are in contact.
According to Ohm's law, . From the expression, the value of the voltage and current ratio is equal to the resistance. In combinations B and C, both the resistances are in parallel, so the voltage-current ratio will be the same for both.
Hence, the correct answer is option 2.
Page No 309:
Question 45:
Four students performed experiments on series and parallel combination of two given resistors R1 and R2 which obey Ohm's law and plotted the following VI graphs:
Which of the graph is correctly labeled in terms of 'series' and 'parallel'?
(1) graph A
(2) graph B
(3) graph C
(4) graph D
Answer:
According to Ohm's law,
From , we can say the graph between 'I' and 'V' will be a straight line, and the slope of the graph will be equal to . Net resistance in series combination is more than the net resistance in parallel combination, hence the slope will be less for series combination and more for the parallel combination.
Hence, the correct answer is option 1.
Page No 309:
Question 46:
You are given four ammeters A, B, C and D having the least counts mentioned below:
(a) Ammeter A with least count 0.25 A
(b) Ammeter B with least count 0.5 A
(c) Ammeter C with least count 0.05 A
(d) Ammeter D with least count 0.1 A
Which of the ammeters would you prefer for doing an experiment to determine the equivalent resistance of two resistance most accurately, when connected in parallel?
(1) A
(2) B
(3) C
(4) D
Answer:
An ammeter with the minimum least count should be used while determining the equivalent resistance of two resistors, so that there should be minimum errors in the experiment.
Hence, the correct answer is option 3.
Page No 309:
Question 47:
Consider the two circuits A and B given alongside :
In the circuits A and B shown here, the voltmeter reading would be :
(1) nearly 4.5 V in both the circuits
(2) 0 V in both the circuits
(3) nearly 1 V for circuit A and nearly 4.5 V for circuit B
(4) 0 V for circuit A and nearly 4.5 V for circuit B
Answer:
As the switch in circuit A is not closed so there will not be any current in the circuit, hence no voltage drop across the resistors. That's why the reading of voltmeter in the circuit will be zero.
The switch is closed in circuit B, as the resistance of the ammeter is taken as negligible, so the voltage across the resistances connected in parallel will be equal to the voltage of the battery. That's why voltage reading in the voltmeter in circuit B will be 4.5 V.
Hence, the correct answer is option 4.
Page No 310:
Question 48:
The values of resistances marked on the coils R1 and R2 are found to be correct. A student connects the given resistors in the following manner (as shown in Figure 1).
He then connects the terminals marked X and Y of the above combination of resistors R1 and R2 to the terminals marked X and Y in the circuit (shown in Figure 2).
The average value of the ratio V/I in the observations recorded in the circuit would be:
(1) 9 Ω
(2) 6 Ω
(3) 3 Ω
(4) 2 Ω
Answer:
According to Ohm's law, the ratio . The net resistance between points X and Y is equal to the net resistance of R1 and R2. As R1 and R2 are connected in series, so the net resistance will be (R1 + R2) = .
Hence the correct option is Option 1.
Page No 310:
Question 49:
A student using the same two resistors, ammeter, voltmeter and battery, sets up two circuits A and B connecting the two resistors first in series and then in parallel.
If the ammeter and voltmeter readings in the two cases be I1, I2 and V1, V2 respectively he is likely to observe that :
(1) I1 = I2 but V1 ≠ V2
(2) I1 < I2 but V1 = V2
(3) I1 > I2 but V1 = V2
(4) I1 = I2 and V1 = V2
Answer:
As the ammeter holds negligible resistance, hence the voltage drop across the resistance is equal to the voltage of the battery. As the battery used in both cases is the same, that's why voltmeter will measure the same value in both the circuits. i.e. V1=V2
In circuit A, both the resistances are connected in series and in circuit B, they are connected in parallel. As the net resistance in circuit A is more than the net resistance in circuit B, and as given the same power supply is used in both the circuits, so the current in circuit A will be less than the current in circuit B.
Hence, the correct answer is option 2.
Page No 310:
Question 50:
Two students made two circuits A and B to determine the resultant resistance of two resistors R1 and R2 connected in series:
All the components have been connected correctly in:
(1) circuit A only
(2) circuit B only
(3) both circuits A and B
(4) neither of the two circuits
Answer:
To determine the resultant resistance between two resistances, the voltmeter should be connected in parallel to both resistances and ammeter should be connected in series in the circuit. In circuit A, both the ammeter and voltmeter are connected correctly but in circuit B, the voltmeter is not connected in parallel across both resistances, so voltmeter is not connected correctly in circuit B.
Hence, the correct answer is option 1.
Page No 311:
Question 51:
Four students have made the following circuit diagrams for determining the equivalent resistance of two resistors connected in series:
The correct circuit diagram is :
(1) A
(2) B
(3) C
(4) D
Answer:
For determining the equivalent resistance of two resistors connected in series, the ammeter is connected in series and the voltmeter is connected in parallel to the resistors. As the current flows from high voltage to low voltage, hence the polarities of ammeter and voltmeter are also set according to the flow of current in the circuit.
Out of all given circuit, only circuit B is correct, as it has both ammeter and voltmeter connected at the right place and with right polarities.
Hence, the correct answer is option 2.
Page No 311:
Question 52:
Consider the following four circuits P, Q, R and S which have been set up to find the resultant resistance of two resistors combined in parallel:
The correct way of connecting the ammeter and voltmeter in the circuit is:
(1) P
(2) Q
(3) R
(4) S
Answer:
For determining the equivalent resistance of two resistors connected in parallel, the ammeter is connected in series and the voltmeter is connected in parallel to the combination of resistors. As the current flows from high voltage to low voltage, so the polarities of ammeter and voltmeter are also set according to the flow of current in the circuit.
Out of all given circuits, only circuit B is correct, as it has both ammeter and voltmeter connected at the right place and with the right polarities.
Hence, the correct answer is option 2.
Page No 311:
Question 53:
In order to determine the equivalent resistance of two resistors R1 and R2 connected in series, a student made this circuit for his experiment.
The only statement which is true for this circuit is that it gives:
(1) incorrect readings for current I as well as for potential difference V
(2) correct reading for current I but incorrect reading for potential difference V
(3) incorrect reading for current I but correct reading for potential difference V
(4) correct readings for both current I and potential difference V
Answer:
For determining the equivalent resistance of two resistors connected in series, the ammeter is connected in series and the voltmeter is connected in parallel to the resistors. As the current flow from high voltage to low voltage so the polarities of ammeter and voltmeter are also set according to the flow of current in the circuit.
In the given circuit the voltmeter is not properly connected but the ammeter is connected in series, hence the circuit will give the correct value of current I, but the incorrect value of potential difference V.
Hence, the correct answer is option 2.
Page No 312:
Question 54:
To find the resultant resistance of two resistors when connected in series, a student arranged the various components according to the circuit shown alongside:
The student, however, did not succeed in his objective. Which of the following mistake has been made by the student in setting up the circuit?
(1) position of voltmeter is wrong
(2) position of ammeter is wrong
(3) terminals of voltmeter are wrongly connected
(4) terminals of ammeter are wrongly connected
Answer:
For determining the equivalent resistance of two resistors connected in series, the ammeter is connected in series and the voltmeter is connected in parallel to the resistors. As the current flows from high voltage to low voltage, so the polarities of ammeter and voltmeter are also set according to the flow of current in the circuit.
In the given circuit terminals of ammeter are wrongly connected as per the direction of flow of current in the circuit.
Hence, the correct answer is option 4.
Page No 312:
Question 55:
The following apparatus is available in the school laboratory:
| Battery | : | 4.5 V |
| Rheostat | : | Varies battery voltage from 0 to 4.5 V |
| Resistors | : | 1 Ω and 2 Ω |
| Ammeters | : | A1 of range 0 to 1 A; Least count 0.05 A |
| : | A2 of range 0 to 3 A; Least count 0.1 A | |
| Voltmeters | : | V1 of range 0 to 5 V; Least count 0.1 V |
| : | V2 of range 0 to 10 V; Least count 0.5 V |
The best combination of ammeter and voltmeter for finding the resultant resistance of the two given resistors connected in series would be:
(1) ammeter A1 and voltmeter V1
(2) ammeter A1 and voltmeter V1
(3) ammeter A2 and voltmeter V1
(4) ammeter A2 and voltmeter V2
Answer:
Maximum battery voltage in the circuit = 4.5 V
The total resistance in series =
Maximum Current that can be flown in the circuit =
For the given set up the only ammeter A2 will be appropriate because it can measure the maximum current in the circuit, while the ammeter A1 can only measure current up to 1 A, so it would not be useful. Also, the voltmeter V1 would be sufficient because it can measure the maximum possible potential difference across the resistors and it has minimum least count.
Hence, the correct answer is option 3.
Page No 312:
Question 56:
The science laboratory in a school has the following apparatus available in it:
| Battery | : | 6 V |
| Rheostat | : | Varies battery voltage from 0 to 6 V |
| Resistors | : | 3 Ω and 6 Ω |
| Ammeters | : | A1 of range 0 to 5 A; Least count 0.25 A |
| : | A2 of range 0 to 3 A; Least count 0.1 A | |
| Voltmeters | : | V1 of range 0 to 10 V; Least count 0.5 V |
| : | V2 of range 0 to 5 V; Least count 0.1 V |
For the experiment to determine the equivalent resistance of the two given resistors connected in parallel, the best combination would be:
(1) ammeter A1 and voltmeter V2
(2) ammeter A2 and voltmeter V1
(3) ammeter A1 and voltmeter V1
(4) ammeter A2 and voltmeter V2
Answer:
Maximum battery voltage possible in the circuit = 6 V
Total resistance of parallel combination =
The Maximum current that can flow in the circuit =
According to given data, the ammeter A2 will perfectly suit for the setup, as it has its maximum range equal to the maximum current possible in the circuit and also the minimum least count.
Also, the voltmeter V1 would be most suitable because it can measure the maximum possible voltage drop across the resistors, whereas the other voltmeter can not.
Hence, the correct answer is option 2.
Page No 312:
Question 57:
The ammeter, voltmeter and, resistors R1 and R2 connected in the circuit as shown below have been checked and found to be correct.
On plugging the key, the voltmeter reads 4.5 V but the ammeter reads 1.5 A. This is most likely because the wires joined to:
(1) resistor R1 and loose
(2) resistor R2 are loose
(3) both the resistors R1 and R1 are loose
(4) ammeter terminals are loose
Answer:
According to the given circuit, Ammeter should read 2.15 A instead of 1.5 A. The reason behind the incorrect reading is that the resistor R2 is loose in the circuit, so the total resistance of the circuit is just equal to the R1, that's why the ammeter is showing a reading of 1.5 A.
Hence, the correct answer is option 2.
Page No 313:
Question 58:
A student determines the focal length of a device X, by focussing the image of a far off object on the screen positioned as shown in the figure alongside.
The device X is a :
(1) Convex lens
(2) Concave lens
(3) Convex mirror
(4) Concave mirror
Answer:
As all the rays are reflected and converged after falling on the device X, and the image is focussed on the screen, the device X is a converging mirror or concave mirror which forms an image of a far off object by converging the rays on its focus.
Hence, the correct answer is option 4.
Page No 313:
Question 59:
The focal length of the concave mirror in the experimental set up, shown alongside, equals:
(1) 10.3 cm
(2) 11.0 cm
(3) 11.7 cm
(4) 12.2 cm
Answer:
A concave mirror converges the rays coming from infinity on its focus and the distance of the focal point from the pole of the mirror is called the focal length. In the given figure, the rays are converging at distance 4.3 cm and the pole of the mirror is at 15.3 cm. That's why the focal length of the given concave mirror = 15.3 cm 4.3 cm = 11.0 cm
Hence, the correct answer is option is 2.
Page No 313:
Question 60:
While determining the focal length of a concave mirror, a student obtained the image of a distant object on a screen. In order to get the focal length of the mirror, the student should measure the distance:
(1) between the object and the mirror only
(2) between the screen and the mirror only
(3) between the object and the screen only
(4) between the screen and mirror as well as between the screen and the object
Answer:
If a student obtains an image of a distant object through a concave mirror on the screen then the distance between the mirror and the screen would simply be the focal length of the concave mirror, as the concave mirror converges all the rays coming from infinity on its focus.
Hence, the correct answer is option 2.
Page No 313:
Question 61:
A student gets a blurred image of a distant object on a screen which is fixed at a place. In order to obtain a sharp image on the screen, he will have to shift the mirror:
(1) towards the screen
(2) away from the screen
(3) either towards or away from the screen
(4) very far away from the screen
Answer:
A concave mirror converges all the rays coming from infinity or from a distant object on its focus and forms a clear image on the screen if placed right at the focus. If the student is getting a blurred image that means he needs to shift the mirror either away or towards the screen so that the focal point can b obtained on the screen and the rays can converge on the screen to form a clear image.
Hence, the correct answer is option 3.
Page No 313:
Question 62:
Four students A, B, C and D performed the experiment to determine the focal length of a concave mirror by obtaining the image of a distant tree on a screen. They measured the distances between the screen and the mirror as shown in the diagrams given below.
The correct value for focal length will be obtained by the student:
(1) A
(2) B
(3) C
(4) D
Answer:
A concave mirror converges all the rays coming from infinity on its focus, the distance of the pole of the mirror from the focus is called the focal length of the mirror.
If students obtain the image of a distant tree on a screen, then the distance of the screen fro the pole of the mirror would give the correct value of the focal length of the mirror. So only student C will get the right value because others are not measuring the distance of the screen from the pole of the mirror properly.
Hence the correct option is Option 3.
Page No 313:
Question 63:
A student has to do the experiment on finding the focal length of a given concave mirror by using a distant object. Out of the following 'set-ups' A, B, C and D available to him:
A : a screen, a mirror holder and a scale
B : a mirror holder, a screen holder and a scale
C : a screen holder and a scale
D : a mirror holder and a scale
The 'set-up' which is likely to give him the best result is :
(1) A
(2) B
(3) C
(4) D
Answer:
To obtain the focal length of a concave mirror, the student needs to form an image of a distant object on a screen using the given mirror and then calculating the distance of the screen from the pole of the mirror. So, he will need a screen, a mirror holder and a scale along with the mirror given.
Hence, the correct answer is option 1.
Page No 314:
Question 64:
Four students A, B, C and D performed an experiment to determine the focal length of a concave mirror by using a lighted candle kept at a considerable distance as the object. They represented the position of image by drawing the following diagrams:
Which diagram describes the correct position of the image of the candle?
(1) A
(2) B
(3) C
(4) D
Answer:
In order to determine the focal length of the mirror, students need to obtain the image at the focal point of the mirror. So, in the above experiment, the image should form at the focus.
Hence, the correct answer is option 4.
Page No 314:
Question 65:
The parallel rays from the top of a distant tree are incident on a concave mirror forming its image on a screen.
The diagram which shows the image of the tree on the screen correctly is:
(1) A
(2) B
(3) C
(4) D
Answer:
When the parallel rays from the top of the tree would fall on the mirror, it would converge them on its focus and an image can be formed on the screen. The image formed at the focus of the concave mirror is always real and inverted in nature. So, the image of the tree will also be inverted when obtained on the screen.
Hence, the correct answer is option 2.
Page No 314:
Question 66:
In order to determine the focal length of a concave mirror, a student obtained a sharp image of the grill of a window in the laboratory wall on a screen. His teacher suggested that to get better result for focal length, he should focus a distant tree instead of the window grill. In which direction should the mirror be moved for this purpose so as to get a sharp image of the tree on the screen?
(1) behind the screen
(2) away from the screen
(3) towards the screen
(4) very far away from the screen
Answer:
The grill of the window is a nearby object for the concave mirror, hence the mirror will always form its image beyond its focal point. But if the object is a distant tree then the concave mirror will converge all the incident rays on its focus and will form a sharp image. So, in order to get the image of a distant tree, screens should be at the focal point of the mirror. That's why the student needs to move the mirror towards the screen.
Hence, the correct answer is option 3.
Page No 314:
Question 67:
In order to determine the focal length of a concave mirror, a student obtained the sharp image of a distant tree on a screen. In order to obtain a sharp image of a window grill of the laboratory on the same screen, in which direction should the screen be moved?
(1) very close to the mirror
(2) very far away from the mirror
(3) slightly nearer to the mirror
(4) slightly farther away from the mirror
Answer:
The concave mirror converges all the rays coming from the distant tree on its focus and forms a sharp image on the screen placed at the focal point of the mirror. So, in order to get the image of a grill of the window, which is a nearby object, the student needs to move the screen away from the mirror, as for any nearby object concave mirror always forms a real image beyond the focus. So, the screen should be moved away from the focal point of the mirror.
Hence, the correct answer is option 4.
Page No 314:
Question 68:
A student performs an experiment on finding the focal length of a convex lens by keeping a lighted candle on one end of laboratory table, a screen on its other end and the lens between them as shown in the figure. The positions of the three are adjusted to get a sharp image of the candle flame on the screen.
If now the candle flame were to be replaced by a distant lamp on a far away electric pole, the student would be able to get a sharp image of this distant lamp on the screen by moving:
(1) The screen in the direction of the lens or the lens in the direction of the screen
(2) the screen in the direction of the lens or the lens away from the screen
(3) the screen away from the lens or the lens in the direction of the screen
(4) neither the screen nor the lens
Answer:
A convex lens always forms the image of a nearby object away from its focus. So, if a student obtained the image of the candle on the screen, that means the screen was away from the focus somewhere.
Now, if he needs to form an image of a distant lamp on the same screen then he needs to move the screen in the direction of the lens or the lens in the direction of the screen in order to place the screen at the focus of the lens, because a convex lens converges all the rays coming from a distant object on its focus.
Hence, the correct answer is option 1.
Page No 315:
Question 69:
A student obtained a sharp image of the grill of a window in the laboratory on a screen, using a convex lens. For getting better results, her teacher suggested focussing of a distant tree instead of the grill. In which direction should the lens be moved for this purpose to get a sharp image on the screen?
(1) Towards the screen
(2) Away from the screen
(3) Behind the screen
(4) Very far away from the screen
Answer:
Grill of the window is a nearby object for the lens, so the image would form away from the focal point of the lens. Now, to obtain the image of a distant tree, he needs to shift the lens towards the screen to have the focal point on the screen. Because the convex lens converges all the rays coming from a distant object to its focal point.
Hence, the correct answer is option 1.
Page No 315:
Question 70:
A sharp image of a distant object is obtained on a screen by using a convex lens. In order to determine the focal length of the lens, you need to measure the distance between the :
(1) lens and the object
(2) lens and the screen
(3) object and the screen
(4) lens and the screen and also between object and the screen
Answer:
A convex lens converges all the rays coming from a distant object on its focus to form a real image. If the image is obtained on a screen placed at the focal point of the lens, then the distance between the lens and the screen would be the focal length of the lens.
Hence, the correct answer is option 2.
Page No 315:
Question 71:
While performing the experiment to determine the focal length of a convex lens by using the sun as the distant object, a student could not find a screen with stand. In the absence of a good screen, which of the following method is the most appropriate and safe to be used by the student?
(1) He should focus the image of the sun on his hand
(2) He should focus the image of the sun on his nylon shirt
(3) He should focus the image of the sun on a wall of the room
(4) He should focus the image of the sun on a carbon paper
Answer:
Sun is very far from the earth, so all the rays coming from the sun become parallel and when they fall on a convex lens, they converge at its focus to form a diminished image. So, if the image would be obtained on either of a hand, nylon shirt or a carbon paper then due to focussed light energy on a single point, the temperature may increase and it can start a fire too. That's why, to avoid any damage or harm, the image of the sun should be obtained on a wall of the room.
Hence, the correct answer is option 3.
Page No 315:
Question 72:
While performing an experiment on determining the focal length of a convex lens, a student obtains a sharp inverted image of the laboratory window grill on the screen and measures the distance between the screen and the lens. She then repeats the experiment and takes a distant tree as the object in the second case. In order to get a sharp image of the tree on the screen, she will now have to move the screen:
(1) slightly nearer to the lens
(2) slightly farther away from the lens
(3) very close to the lens
(4) very far away from the lens
Answer:
The grill of the window is a nearby object for the lens, so the image would form away from the focal point of the lens. Now, to obtain the image of a distant tree, she needs to move the screen towards the lens in order to obtain the focal point of the lens on the screen because the convex lens converges all the rays coming from a distant object at its focal point to form a real image.
Hence, the correct answer is option 1.
Page No 315:
Question 73:
While performing the experiment on the determination of focal length of a convex lens, four student obtained the image of the same distant tree on the screen:
Which diagram shows the formation of image correctly?
(1) A
(2) B
(3) C
(4) D
Answer:
When the rays coming from a distant object are converged through a convex lens to form an image on its focus, the image formed at focus is real and inverted in nature. So, the image of a distant tree would be inverted if focussed through a convex lens to form a clear image on a screen placed at the focal point of the lens.
Hence, the correct answer is option 4.
Page No 315:
Question 74:
A student was given the following suggestions by his classmates for performing the experiment on finding the focal length of a convex lens:
(A) Select any object very far away from the laboratory window
(B) Select a well illuminated object far (but not very far) from the laboratory window
(C) Keep all the lights of the laboratory on
(D) Place the lens between the object and the screen
(E) Place the screen between the object and the lens
(F) Obtain the sharpest image of the object on the screen
He can perform the experiment better by following the suggestions:
(1) A, D, F
(2) B, C, E
(3) C, F, B
(4) D, F, B
Answer:
A convex lens converges all the rays coming from a distant object to form a sharp image on its focal point. If a screen is placed behind the lens and a sharp image of a distant object is obtained on the screen then the distance of the screen from the pole of the lens will be the focal length of the lens.
So, the student needs to select any object very far away from the laboratory and place the lens between the object and the screen. If he obtains a sharp image of the object on the screen, then the distance of the screen from the lens would give the focal length of the lens.
Hence, the correct answer is option 1.
Page No 316:
Question 75:
For performing an experiment, a student was asked to choose one concave mirror and one convex lens from a lot of mirrors and lenses of different kinds. the correct procedure adopted by her will be:
(1) To choose a mirror and lens which can form an enlarged and erect image of an object.
(2) To choose a mirror which can form a diminished and erect image and a lens which can form an enlarged and erect image of the object.
(3) To choose a mirror which can form an enlarged and erect image and a lens which can form a diminished and erect image of an object.
(4) To choose a mirror and a lens which can form a diminished and erect image of an object.
Answer:
When a concave mirror forms a diminished image, it's always inverted. When it forms an erect image, it's always enlarged. A convex lens also forms an enlarged erect image. So, both the concave mirror and the convex lens can form an erect and an enlarged image of the object.
That's why, to have one concave mirror and one convex lens, the student should choose a mirror and a lens which can form an enlarged and erect image of the object.
Hence, the correct answer is option 1.
Page No 316:
Question 76:
A teacher gives a convex lens and a concave mirror of focal length of about 20 cm each to his student and ask him to find their focal lengths by obtaining the image of a distant object. The student uses a distant tree as the object and obtains its sharp image, one by one, on a screen. The distance d1 and d2 between the lens/mirror and the screen in the two cases and the nature of their respective sharp images are likely to be:
(1) (20 cm, 40 cm) and (erect, erect)
(2) (20 cm, 40 cm) and (inverted, erect)
(3) (20 cm, 20 cm) and (inverted, inverted)
(4) (20 cm, 20 cm) and (erect, inverted)
Answer:
A convex lens and a concave mirror both converges the rays coming from a distant object to their focal point to form an inverted image. If images formed by them are obtained on a screen, then the distance of the screen from the lens or the mirror would be the focal length of the lens or the mirror respectively.
Similarly, in the given case, the distances d1 and d2 are the focal lengths of the given convex lens and concave mirror respectively and the nature of the image would be inverted for both lens and the mirror.
Hence, the correct answer is option 3.
Page No 316:
Question 77:
Three students measured the focal length of a convex lens using parallel rays from a distant object. All of them measured the distance between the lens and the inverted image on the screen.
(i) Student A saw a sharp image on the screen and labelled the distance as f1
(ii) Student B saw a slightly larger blurred image on the screen and labelled the distance as f2
(iii) Student C saw slightly smaller blurred image on the screen and labelled the distance as f3
The relation between the three measurements would most likely be
(1) f1 = f2 = f3
(2) f1 < f2 < f3
(3) f3 < f1 < f2
(4) f1 < f2 and f1 = f3
Answer:
A convex mirror converges all the rays coming from the distant object on its focus. According to given conditions, we can say if a sharp image is obtained at f1, then f1 must be the focal point of the lens. Now if the distance between the screen and the lens is varied then beyond the focus f1, the image obtained would be large and blurred and behind the focus f1, the image would be smaller and blurred.
Hence, the correct answer is option 3.
Page No 316:
Question 78:
A student has to do the experiment on finding the focal length of a given convex lens by using a distant object. She can do her experiment if she is also made available:
(1) a lamp and a screen
(2) a scale and a screen
(3) a lamp and a scale
(4) only a screen
Answer:
A convex lens converges all the rays coming from a distant object and forms a sharp image on the screen placed at the focal point of the lens. To obtain the focal length, the student needs to have a screen to obtain an image of a distant object and a scale to measure the distance of the screen from the lens.
Hence, the correct answer is option 2.
Page No 316:
Question 79:
A student performs an experiment to estimate the focal length of a convex lens by obtaining the image of a distant window on a white screen. The image formed on the white screen is :
(1) virtual, erect and magnified
(2) real, erect and magnified
(3) real, inverted and diminished
(4) virtual, inverted and diminished
Answer:
Convex lens converges all the rays coming from a distant object to its focus to form a sharp image. The image obtained is real as it can be obtained on a screen placed on the focus of the lens, also the image formed is diminished and inverted in nature.
Hence, the correct answer is option 3.
Page No 316:
Question 80:
Four students A, B, C and D performed an experiment to determine the focal length of a convex lens by using a lighted candle kept at a considerable distance as the object. They represented the position of image by drawing the following diagrams:
Which diagram describes the correct position of image of the candle?
(1) A
(2) B
(3) C
(4) D
Answer:
A convex lens converges the rays coming from a distant object to form a sharp image on its focus. In order to determine the focal length of the lens, students need to obtain the image of a distant object at the focal point of the lens. So, in the above experiment, the image should form at the focus.
Hence, the correct answer is option 3.
Page No 317:
Question 81:
A student performs the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He measures the angle of incidence ∠i, angle of refraction ∠r and angle of emergence ∠e for all his observations. He would find that in all cases:
(1) ∠i is more than ∠r but (nearly) equal to ∠e
(2) ∠i is less than ∠r but (nearly equal to ∠e
(3) ∠i s more than ∠e but (nearly) equal to ∠r
(4) ∠i is less than ∠e but (nearly) equal to ∠r
Answer:
When a ray travels from a rarer medium to denser medium(Air to glass) it bends towards the normal, so the incidence angle is always more than the angle of refraction. But, when it travels from denser medium to rarer medium(Glass to air) then it bends away from the normal and becomes parallel to the incident ray, so the angle of emergence is (nearly) equal to the angle of incidence.
Hence, the correct answer is option 1.
Page No 317:
Question 82:
A student does the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He can get a correct measure of the angle of incidence and the angle of emergence by following the labelling indicated in figure:
(1) A
(2) B
(3) C
(4) D
Answer:
The angle formed by the incident ray and the normal to the rectangular slab is taken as the angle of incidence and the angle formed by the emergent ray and the normal is taken as the angle of emergence. According to this, the only figure showing the correct angle of incidence and emergence is figure D.
Hence, the correct answer is option 4.
Page No 317:
Question 83:
A student suggested the following 'guidelines' to his friend for doing the experiment on tracing the path of a ray of light passing through a rectangular glass slab for three different angles of incidence:
A. Draw the 'outline' of the glass slab at three positions on the drawing sheet.
B. Draw 'normals' on the top side of these 'outlines' very near their left end.
C. Drawn the incident rays on the three 'outlines' in directions making angles of 30°, 45°, 60° with the normals drawn.
D. Fix two pins vertically on each of these incident rays at two points nearly 1 cm apart.
E. Look for the images of the 'heads' of these pins while fixing two pins from the other side, to get the refracted rays.
When he showed these 'guidelines' to his teacher, the teacher corrected and modified the 'guidelines' labelled as
(1) B, C, E
(2) B, D, E
(3) B, C, D
(4) C, D, E
Answer:
The guidelines which need to be modified are B, D, and E.
Because one should need to draw the 'normals' on the top side, very near their left end and also at the bottom, very near the right end. The distance between the pins should be 6 cm, not 1 cm to trace the path more accurately and also while fixing the other two pins on the other side, we need to look for the head of the pins such that they all be in a straight line, which helps us to get the path of the emergent rays not refracted rays.
Hence, the correct answer is option 2.
Page No 317:
Question 84:
A student traces the path of a ray of light passing through a rectangular glass slab.
For measuring the angle of incidence, he must position the protractor in the manner shown in figure:
(1) A
(2) B
(3) C
(4) D
Answer:
The angle of incidence is the angle formed by the incident ray and the normal to the slab. So, only in figure B, the correct measurement of the angle of incidence has been shown.
Hence, the correct answer is option 2.
Page No 317:
Question 85:
A student performed the experiment of glass slab and with different angles of incidence measured the angles of refraction and emergence in each case. He then recorded his observations as given in the table.
The correct observation is
| S. No. | Angle of incidence | Angle of refraction | Angle of emergence |
| A B C D |
30° 40° 50° 60° |
25° 42° 50° 60° |
30° 40° 50° 62° |
(1) A
(2) B
(3) C
(4) D
Answer:
When a ray passes through a glass slab, it bends towards the normal. So, the angle of the incidence is always greater than the angle of refraction. The same light ray bends away from the normal and becomes parallel to the incident ray, when it emerges from the slab in the air. So, the angle of emergence is always equal to the angle of incidence. According to this, only student A has made correct observations.
Hence, the correct answer is option 1.
Page No 318:
Question 86:
Four students A, B, C and D showed the following traces of the path of a ray of light passing through a rectangular glass slab.
The trace most likely to be correct is that of student:
(1) A
(2) B
(3) C
(4) D
Answer:
When a ray is passed through a rectangular glass slab, it bends towards the normal and when it emerges from the glass slab it bends away from the normal and becomes parallel to the incident ray but with a lateral shift. A laterally shifted ray parallel to the incident ray can only be seen in diagram B.
Hence, the correct answer is option 2.
Page No 318:
Question 87:
In an experiment on tracing the path of a ray of light through a rectangular glass slab, four students A, B, C and D used the following values of the angle of incidence and the distance between the feet of the two pins (fixed on the incident rays):
(A) 30°, 45°, 60° and 1 cm
(B) 30°, 45°, 60° and 6 cm
(C) 20°, 50°, 80° and 10 cm
(D) 20°, 50°, 80° and 15 cm
Out of these, the best choice is that of the student:
(1) A
(2) B
(3) C
(4) D
Answer:
The best choice of angles of incidence would be 30°, 45°, and 60°, because it would be easier to perform the calculations to obtain the angle of refraction theoretically. Also, the best choice for the distance between the pins would be 6 cm, because it will provide a better line of sight for the observations through the other side of the slab.
Hence, the correct answer is option 2.
Page No 318:
Question 88:
A student while doing the experiment on tracing the path of a ray of light passing through a rectangular glass slab measured the three angles marked as θ1, θ2 and θ3 in the figure.
His measurements could be correct if he were to find:
(1) θ1 < θ2 < θ3
(2) θ1 < θ2 but θ1 = θ3
(3) θ1 > θ2 > θ3
(4) θ1 > θ2 but θ2 = θ3
Answer:
When a light ray enters the rectangular glass slab, which is denser medium than air, it bends towards the normal. When it emerges back to the rarer medium(air), it bends away from the normal and becomes parallel to the incident ray. So, the angle of incident is always greater than the angle of refraction and always equal to the angle of emergence. i.e.
According to this, the correct relation between the given angles is,
Hence, the correct answer is option 2.
Page No 318:
Question 89:
In the experiment on tracing the path of a ray of light passing through a rectangular glass slab, the correct setting of the protractor (D), for measuring the angle of incidence (∠i), and the angle of emergence (∠e) correspond, respectively, to diagrams:
(1) K and M
(2) K and N
(3) L and M
(4) L and N
Answer:
The angle of incidence is given by the angle between the incident ray and the normal and the angle of emergence is given by the angle between the emergent ray and the normal to the slab. According to this, the correct diagrams for measurement of the angle of incidence and angle of emergence are K and M respectively.
Hence, the correct answer is option 1.
Page No 318:
Question 90:
Four students A, B, C and D selected the following items from the materials available in the science laboratory to perform an experiment to study the refraction of light through a glass slab:
(A) convex lens, glass slab, pins, drawing board, white paper, scale
(B) glass slab, pins, drawing board, scale, white paper, protractor
(C) glass slab, glass prism, candle, screen, pins, scale, drawing board, protractor
(D) concave mirror, pins, glass slab, protractor, white paper, drawing board
Correct choice of the items required is made by the student:
(1) A
(2) B
(3) C
(4) D
Answer:
To study the refraction of light through a glass slab, one needs a drawing board to perform the experiment, a scale to measure the path lengths, white paper to trace the path, pins to mark the path of the light ray, and a protractor to measure the angles.
Hence, the correct answer is option 2.
Page No 318:
Question 91:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, four students measured the angles of incidence (i), angles of refraction (r) and angles of emergence (e) as shown in the diagrams:
The correct measurement is given in the diagram:
(1) A
(2) B
(3) C
(4) D
Answer:
The angle of incidence is taken as the angle between the incident ray and the normal, the angle of refraction is taken as the angle between the refracted ray and normal, and the angle of emergence is taken as the angle between the emergent ray and the normal to the slab. According to this, we can say that the correct representation is given by student C.
Hence, the correct answer is option 3.
Page No 318:
Question 92:
A teacher asked four students to record the observations of the experiment on tracing the path of a ray of light through a rectangular glass slab. The students recorded their observations under the following headings:
(1) Angle of incidence, Angle of refraction, Angle of reflection
(2) Angle of incidence, Angle of deviation, Angle of emergence
(3) Angle of incidence, Angle of reflection, Angle of emergence
(4) Angle of incidence, Angle of refraction, Angle of emergence
The correct observations were recorded by the student:
(1) A
(2) B
(3) C
(4) D
Answer:
When a light ray is passed through a rectangular glass slab, it suffers refraction and bends towards the normal. The same exits from the slab by bending away from the normal and becomes parallel to the incident ray. So, to trace the path of the light ray through a rectangular glass slab, we must observe the angle of incidence, angle of refraction, and the angle of emergence.
Hence, the correct answer is option 4.
Page No 318:
Question 93:
An experiment for tracing the path of a ray of light through a glass slab was set up in the laboratory and ray diagram was drawn as shown here. The teacher asked the students to identify the refracted ray. The correct answer is :
(1) SR
(2) RQ
(3) N1N2
(4) QP
Answer:
When a light ray is passed through a rectangular glass slab, it refracts at the boundary of the slab and bends towards the normal. So, in the given figure, SR is the incident ray falling on the glass slab and RQ is the refracted ray bending towards the normal upon entering the slab.
Hence, the correct answer is option 2.
Page No 318:
Question 94:
A student traces the path of a ray of light passing through a rectangular glass slab for three different values of angle of incidence (∠i) namely 30°, 45° and 60°. He extends the direction of incident ray by a dotted line and measures the perpendicular distance 'l' between the extended incident ray and the emergent ray. He will observe that:
(1) 'l' keeps on increasing with increase in angle of incidence
(2) 'l' keeps on decreasing with increase in angle of incidence
(3) 'l' remains the same for all three angles of incidence.
(4) 'l' is the maximum for ∠i = 45° and is less than this value both for ∠i = 30° and ∠i = 60°
Answer:
The perpendicular distance 'l' between the extended incident ray and the emergent ray is known as the lateral shift. Lateral shift is directly proportional to the sine of the angle of incidence. i.e.
So, lateral shift increases as the angle of incidence increases.
Hence, the correct answer is option 1.
Page No 318:
Question 95:
A ray of light is incident on a parallel-sided glass slab as shown in the figure. The angle of refraction for this ray of light is likely to be:
(1) 60°
(2) 33°
(3) 57°
(4) 30°
Answer:
In the given figure, we can see that angle of refraction ( ) and angle of form a pair of alternate opposite angles, so both are equal.
The angle of refraction, ( Alternate opposite angles)
Hence, the correct answer is option 2.
Page No 320:
Question 96:
In an experiment to study the refraction of light through a rectangular glass slab, a student measured the angle of incidence, angle of refraction and the angle of emergence. The student lost the reading of angle of incidence but noted the readings of angle of refraction to be 35° and angle of emergence to be 65°. The angle of incidence is likely to be:
(1) 45°
(2) 55°
(3) 35°
(4) 65°
Answer:
When a light ray refracts through a rectangular glass slab, the angle of incidence and the angle of emergence are always equal. That's why, the angle of incidence will be 65°, equal to the given angle of emergence.
Hence, the correct answer is option 4.
Page No 320:
Question 97:
In the glass slab experiment, a student measures the angle of incidence (∠i) in air and finds it to be 40°. He also measured the corresponding angle of refraction as well as the angle of emergence for this ray of light but lost their record. The most likely record of readings for the angle of refraction and angle of emergence will be:
(1) ∠r = 40° and ∠e = 50°
(2) ∠r > 40° and ∠e = 40°
(3) ∠r = 50° and ∠e = 40°
(4) ∠r < 40° and ∠e = 40°
Answer:
When a light ray enters a glass slab then it bends towards the normal, so the angle of refraction becomes smaller than the angle of incidence. But, when it emerges from the slab into the air again, it bends away from the normal and becomes parallel to the incident ray, such that the angle of the emergence becomes equal to the angle of incidence.
Hence. the correct answer is option 4.
Page No 320:
Question 98:
In the experiment to trace the path of a ray of light through a parallel sided glass slab, a student measured the angles of refraction for three different angles of incidence. He will find that:
(1) angle of refraction is always equal to the angle of incidence
(2) angle of refraction is always smaller than the angle of incidence
(3) angle of refraction is always greater than the angle of incidence
(4) angle of refraction can be smaller or greater than the angle of incidence depending on the refractive index of glass slab
Answer:
When a light ray enters a glass slab, it bends towards the normal due to change in the medium from rarer to denser. So, the angle of refraction is always smaller than the angle of incidence.
Hence, the correct answer is option 2.
Page No 320:
Question 99:
Which of the following is the best set-up for tracing the path of a ray of light through a rectangular glass slab?
(1) A
(2) B
(3) C
(4) D
Answer:
While tracing the path of the light ray passing through a rectangular glass slab, the pins should be pointed at a distance of at least 6 cm and the angle of incidence should be kept around . Because it will provide a better line sight to observe the path of the ray, from the other side of the slab.
Hence, the correct answer is option 2.
Page No 320:
Question 100:
A student performs an experiment with glass slab to trace the path of a ray of light entering from air into glass slab and emerging into air again. On looking carefully at the trace obtained on paper, he will observe that the emergent ray and the incident ray:
(1) are converging (coming closer to each other)
(2) are diverging (moving away from each other)
(3) are perpendicular (at right angles to each other)
(4) are parallel (at equidistant from each other)
Answer:
When a light ray enters a glass slab, it bends towards the normal. But when it emerges in the air again, it bends away from the normal and becomes parallel to the incident ray. So, the student will observe that the emergent ray and the incident ray are parallel.
Hence, the correct answer is option 4.
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