Lakhmir Singh Manjit Kaur Physics 2020 2021 for Class 10 Science Chapter 10 - Model Test Paper 3

Answer:

Used clothes and newspaper can be recycled.

Answer:

Alloys are used in electrical heating devices rather than pure metals because the resistivity of an alloy is more than the resistivity of pure metal. Also, the melting point of an alloy is high, so it does not melt or oxidize easily even at a higher temperature.

Answer:

The phenomena responsible for the formation of a coating on copper and silver objects is known as corrosion. Silver turns black due to the formation of silver sulphide$\left({\mathrm{Ag}}_2\mathrm{S}\right)$ while copper turns green due to the formation of a mixture of copper carbonate and copper hydroxide$\left[\right({\mathrm{CuCO}}_3).(\mathrm{Cu}\left(\mathrm{OH}{)}_2)\right]$.
$2\mathrm{Cu}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}\to \left[\right({\mathrm{CuCO}}_3).(\mathrm{Cu}\left(\mathrm{OH}{)}_2\right)]$
$2\mathrm{Ag}+{\mathrm{H}}_2\mathrm{S}\to {\mathrm{Ag}}_2\mathrm{S}+{\mathrm{H}}_2$

Answer:

The metals and alloys have very low resistivity in the range of 10^-8 Ωm to 10^-6  Ωm. So, they are a good conductor of electricity. While insulators have a resistivity of the order of 10¹²  Ωm to 10¹⁷ Ωm. Alloys have generally higher resistivity than its constituent metals and consider good for the heating elements. So, elements C and E are best for making heating elements. While D and F are considered as an insulator and A and B are a good conductor of electricity.  

Answer:

(a) The structures mentioned above have the same origin but they perform same or different functions in different organisms. This indicates that they have evolved from a common ancestor.
(b) The term given to these structures is homologous structures.

Answer:

Answer:

The compound prepared from gypsum which has hardening property when mixed with water is "Plaster of Paris". The chemical formula of Plaster of Paris is ${\mathrm{CaSO}}_4.\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\mathrm{H}}_2\mathrm{O}$.
The balanced chemical equation for the preparation of Plaster of Paris is:
$2{\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}\stackrel{\mathrm{heat}}{\to }2{\mathrm{CaSO}}_4.\frac{1}{2}{\mathrm{H}}_2\mathrm{O}+3{\mathrm{H}}_2\mathrm{O}$

In hospitals, it is used as a plaster for supporting the broken or fractured bones.

Answer:

(a) When zinc granules react with dilute sulphuric acid in a flask, hydrogen gas is evolved and zinc sulphate solution is formed.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

(b) When potassium iodide is added to lead nitrate solution (colourless and clear), a yellow precipitate of lead iodide solution is formed.
$\mathrm{Pb}\left({\mathrm{NO}}_3{)}_2\right(\mathrm{aq})+2\mathrm{KI}(\mathrm{aq})\to {\mathrm{PbI}}_2(\mathrm{s})+2{\mathrm{KNO}}_3(\mathrm{aq})$

(c) When quick lime reacts with water, slaked lime is formed along with release of a large amount of heat, causing a change in temperature in the reaction mixture.
$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{aq})+\mathrm{Heat}$

Answer:

pH has great importance in our daily life:

(a) pH and plants:
Plants require a specific pH for growth. It cannot grow in too acidic soils. If soil is too acidic then its pH can be increased by adding lime:
$CaO+H_{2}S{O}_4\to CaS{O}_4+H_{2}O$
And on the other hand, if the soil is too alkaline then its pH decreases by adding gypsum.

(b) pH and blood or digestive system:
The pH of blood is tightly regulated in the range of 7.2-7.4 and medium in our stomach is highly acidic(pH = 1.2). Sometimes stomach produces too much hydrochloric acid, it causes irritation or pain.

(c) pH and skin:
The acidic pH of the skin prevents colonisation by bacteria. Thus, it acts as a defense against infection.
 

Answer:

(a) The focal length of the eye lens is more when the ciliary muscles of a normal eye are in their most relaxed state. In this state the lens becomes thin.

(b) As the power of a lens is inversely proportional to its focal length. Hence, the power of the eye lens would be more when the focal length would be minimum, which happens when ciliary muscles are in the most contracted state. In this case, the lens becomes thick. 

Answer:

(a) In the circuit, there is a 4-ohm resistor in series with the parallel combination of two 8-ohm resistors.

Total resistance of parallel combination = $\frac{8\times 8}{8+8}=\frac{64}{16}=4 \text{Ω}$

So, net resistance of the circuit = $4 \text{Ω + }4 \text{Ω = 8} \text{Ω}$

(b) Current in the circuit = $\frac{\mathrm{Voltage}}{\mathrm{Net} \mathrm{Resistance}}\text{=}\frac{6 \text{V}}{8 \text{Ω}}\text{= 0.75 A}$

(c) The voltage across the 4-ohm resistor = $0.75 \text{A × 4 Ω= 3 V}$

So, the voltage across parallel combination = $6 \text{V - 3 V = 3 V}$

Answer:

Geothermal energy is the energy obtained from the earth(geo). Generally, from the hot rocks present inside the earth. This energy is used to generate electricity. The hot rocks inside the earth convert the water into steam, the hot steam is then piped out and is used to rotate a turbine that activates a generator, which produces electricity. 

Advantages of geothermal energy:
1) It is a renewable source of energy. 
2) By far, it is non-polluting and environment-friendly.  
3) The maintenance cost of geothermal power plants is very less.  

Answer:

Trophic level of an organism is the position it occupies in a food chain. 

Grass (Producer) →Grasshopper (Primary consumer) →Rat (Secondary consumer) →Owl (Tertiary consumer)

Answer:

The three R’s that need to be practiced in order to save the environment are:

• Reduce: Reducing the usage of resources will help save them for the future. E.g.: reducing usage of electricity by switching off fans and lights when not in use.

• Recycle: Plastics, paper, and glass can be recycled to make other objects.

• Reuse: Using things again and again. For example, jam bottles made of glass can be used to store salt, sugar, oil, etc.

Answer:

(a) A gene is a unit of inheritance that is transferred from the parent to the offspring. It controls the expression of a character. The gene which can express its character even when it is present as a single copy is called a dominant gene. Also it is able to express its characters in all the generations. 
However, a gene which can express its character, only when it is present in pairs is called a recessive gene.

(b) (i) BB - brown eyes
(ii) bb - blue eyes
(iii) Bb - brow eyes

Answer:

(a) Achievements of the Mendeleev's periodic table are as under: (You can write any two)
(i) The systematic study of elements
(ii) Prediction of new elements
(iii) Correction of atomic mass

Elements were classified on the basis of hydrides and oxides formed by elements.

(b) Element X with electronic configuration is 2, 8 ,2 
So the number of valence electrons of X = 2
Number of valence electrons = valency of X
Valency of the nitrate ions (NO₃)^- = 1, so compound formed with element X and nitrate will be M(NO₃)_2.
Valency of the sulphate ions (SO₄)^-2 = 2, so compound formed with element X and sulphate will be MSO_4.
Valency of the phosphate ions (PO₄)^-3 = 3, so compound formed with element X and phosphate will be M₃(PO₄)_2.

(c) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the second group of the periodic table.
It will form an ionic bond, to attain noble gas configuration it will easily lose two electrons.

(d) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the third period of the periodic table.

(e) The atomic number of element X is 12, which resembles magnesium (Mg) of the periodic table.
Another element which belongs to the same period will be sodium (Na).

Answer:

When A, B, C, and D are reacted with iron sulphate, then only B will displace iron from iron sulphate. Hence, B is more reactive than iron.
When A, B, C, and D are reacted with copper sulphate, then only A will displace copper from copper sulphate. Hence, A is more reactive than copper.
When A, B, C, and D are reacted with zinc sulphate, then no reaction takes place. Hence, C is less reactive than iron, copper, and zinc.
When A, B, C, and D are reacted with silver nitrate, then only C will displace silver from silver nitrate. Hence, C is more reactive than silver.
D is less reactive than iron, copper, zinc, and silver.

(a) So, from the following results, we can conclude that B is the most reactive metal.

(b) When B is added to the copper sulphate solution then it will displace copper from copper sulphate.

(c) Increasing order of reactivity of A, B, C, and D is:
D < C < A < B.

(d) As D is less reactive from all the metal, so D can be used as a container to store zinc sulphate and silver nitrate solutions.

(e) Zinc sulphate can be easily stored in a container made up of these metals.
 

Answer:

(a) Power of a lens is given by reciprocal of its focal length. i.e. $P=\frac{1}{f(\text{in} \text{meter)}}$

A negative power means a negative focal length and positive power means positive focal length. As we know, a converging or convex lens has a positive focal length and a diverging or concave lens has a negative focal length. Therefore,
(i) The lens with positive power '+2D' is a converging lens
(ii) The lens with negative power '−4 D' is a diverging lens in nature.

(b) (i) Power of the lens = +2D,  $P=\frac{1}{f(\text{in} \text{meter)}}$

Focal length $=\frac{1}{P}=\frac{1}{2}\text{ m }=50 \text{cm}$

Object distance = $-$100 cm

Using the lens formula,

$$\begin{gathered} \frac{1}{v}-\frac{1}{(-100)}=\frac{1}{50} \\ \Rightarrow \frac{{\displaystyle 1}}{{\displaystyle v}}=\frac{{\displaystyle 1}}{{\displaystyle 100}} \\ \Rightarrow v= 100 \text{cm} \end{gathered}$$

So, the image distance for the first lens is 100 cm. 

Magnification of the lens = $\frac{v}{u}=\frac{100 \text{cm}}{-100 \text{cm}}=-1$

(ii) Power of the lens = -4D,  $P=\frac{1}{f(\text{in} \text{meter)}}$

Focal length $=\frac{1}{P}=-\frac{1}{4}\text{ m }=-25 \text{cm}$

Object distance = $-$100 cm

Using the lens formula,

$$\begin{gathered} \frac{1}{v}-\frac{1}{(-100)}=-\frac{1}{25} \\ \Rightarrow \frac{{\displaystyle 1}}{{\displaystyle v}}=-\frac{{\displaystyle 1}}{{\displaystyle 20}} \\ \Rightarrow v= -20 \text{cm} \end{gathered}$$

So, the image distance for the second lens is $-$25 cm. 

Magnification of the lens = $\frac{v}{u}=\frac{-25 \text{cm}}{-100 \text{cm}}=\frac{1}{4}=0.25$

Answer:

In a household electric circuit different appliances are connected in parallel to one another so that:

(i) The appliances can be operated independently. 
(ii) They get the same applied voltage.


We know that power, $P = V I$

Now, the current flowing through the circuit will be, $I =\frac{ P }{ V}$

Here, P = 1.5 kW = 1500 W

V = 220 volts

So, $I = \frac{1500}{220} =6.81 \text{A}$

As we can see the current flowing the circuit is more than the maximum current rating of the fuse. This means, that the fuse will blow (or melt) and the circuit will break. Therefore, no current will flow further in the circuit.

Answer:

(a)

Function of cerebellum − It helps to maintain posture, equilibrium, and coordination in voluntary movements.

Function of medulla −It helps to control our involuntary muscles such as cardiac, respiratory, etc. It controls the activities of internal organs

Answer:

(a) 


(b) Pollination is the process in which the transfer of pollen grains takes place from anther to stigma for the purpose of fertilization in plants. 

Pollination can occur by two ways -

• Self pollination: When the pollen reaches the stigma of the same flower, the process is known as self pollination.

• Cross pollination: When the pollen reaches the stigma of a different flower on the same plant, or the flower of a different plant of the same kind, the process is known as cross-pollination.

(c) Fertilisation is the process of fusion of male and female gametes. In plants this process is called as double fertilisation. It is a characteristic feature of flowering plants. In this process, out of the two sperm nuclei, one sperm nucleus fuses with the egg nucleus to form an embryo (this process is called syngamy) and another fuses with the polar nucleus to form an endosperm (this process is called triple fusion). Because two kinds of fusion, syngamy and triple fusion, take place, the process is known as double fertilisation.



(d) After the process of fertilisation, the following changes take place.

• The ovary gives rise to the fruit while the other structures of the flower fall down.

• The ovules present inside the ovary develop into seeds. Seeds contain an embryo, which is protected by the seed coat.

Answer:

Observation (i) is wrong because the deflection of a compass needle by the current-carrying straight conductor depends upon the magnetic field around it. So, it is the magnetic field produced by the current-carrying conductor which deflects the compass needle. Therefore, if we reverse the direction of current flowing in the conductor then the deflection of the magnetic needle would also be in the opposite direction. 

Observation (ii) is correct because magnetic field strength decreases as we move away from the conductor. So, the deflection would decrease too.

Answer:

(i) To obtain a resultant resistance of 12-ohms, we can directly connect all the resistances in series. The net resistance of the series combination is simply the sum of all the resistances. Which is, in this case, would be 12-ohms.



(ii) To get a resultant resistance of 3-ohms, we can connect 2-ohm and 4-ohm resistors in series and then we can connect that series combination in parallel with 6-ohm resistor. By doing this, we can get a total of 3-ohm resistance, because the net resistance in series would be 6-ohms and then net resistance of the parallel combination of two 6-ohm resistors would be 3-ohms.

Answer:

(i) When a student keeps a strip of zinc metal in copper sulphate, displacement reaction will take place. Zinc is more reactive than copper sulphate, so zinc will displace copper from copper sulphate and form zinc sulphate.

 $\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

(ii) When a student keeps a strip of copper metal in iron sulphate, no reaction will take place. Copper is less reactive than iron so it will not be able to displace iron from iron sulphate.

$\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)\to \mathrm{No} \mathrm{reaction}$

Answer:

(a) The reaction of C₂H₄O₂ with baking soda will produce carbon dioxide gas which turns lime water milky.

${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{NaHCO}}_3\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

(b) The functional group present in the organic compound will be carboxylic acid (COOH).

(c) The name of the molecule will be ethanoic acid and the molecular formula of organic compound will be CH₃COOH.
 

Answer:

The above experimental setup is used to determine the response of plant parts towards sunlight. The bending of shoot in the direction of sunlight is termed as phototropism.

Answer:

(a) When the plant is kept in dark, the starch which is already present in the plant gets used up.
(b) This process is known as destarching.
(c) The process of cell metabolism in plants requires starch.
(d) The process of photosynthesis does not occur when the plant is kept in the dark room. Photosynthesis is the process by which plants synthesise glucose which is eventually stored as starch.