Board Paper of Class 12-Science 2020 Physics Delhi(Set 3) - Solutions
General Instructions:
Read the following instructions very carefully and strictly follow them:
(i) This question paper comprises four sections – A, B, C and D.
(ii) There are 37 questions in the question paper. All questions are compulsory.
(iii) Section A : Q. no. 1 to 20 are very short-answer type questions carrying 1 mark each.
(iv) Section B : Q. no. 21 to 27 are short-answer type questions carrying 2 marks each.
(v) Section C : Q. no. 28 to 34 are long-answer type questions carrying 3 marks each.
(vi) Section D : Q. no. 35 to 37 are also long answer type questions carrying 5 marks each.
(vii) There is no overall choice in the question paper. However, an internal choice has been provided in two questions of one mark, two questions of two marks, one question of three marks and all the three questions of five marks. You have to attempt only one of the choices in such questions.
(viii) However, separate instructions are given with each section and question, wherever necessary.
(ix) Use of calculators and log tables is not permitted.
(x) You may use the following values of physical constants wherever necessary.
c = 3 × 108 m/s
Read the following instructions very carefully and strictly follow them:
(i) This question paper comprises four sections – A, B, C and D.
(ii) There are 37 questions in the question paper. All questions are compulsory.
(iii) Section A : Q. no. 1 to 20 are very short-answer type questions carrying 1 mark each.
(iv) Section B : Q. no. 21 to 27 are short-answer type questions carrying 2 marks each.
(v) Section C : Q. no. 28 to 34 are long-answer type questions carrying 3 marks each.
(vi) Section D : Q. no. 35 to 37 are also long answer type questions carrying 5 marks each.
(vii) There is no overall choice in the question paper. However, an internal choice has been provided in two questions of one mark, two questions of two marks, one question of three marks and all the three questions of five marks. You have to attempt only one of the choices in such questions.
(viii) However, separate instructions are given with each section and question, wherever necessary.
(ix) Use of calculators and log tables is not permitted.
(x) You may use the following values of physical constants wherever necessary.
c = 3 × 108 m/s
h = 6.63 × 10–34 Js
e = 1.6 × 10–19 C
μo = 4π × 10–7 T m A–1ε0 = 8.854 × 10–12 C2 N–1 m–2
= 9 × 109 N m2 C–2
Mass of neutron = 1.675 × 10–27 kg
Mass of proton = 1.673 × 10–27 kg
Avogadro’s number = 6.023 × 1023 per gram mole
Boltzmann constant = 1.38 × 10–23 JK–1- Question 1
A biconcave lens of power P vertically splits into two identical plano concave parts. The power of each part will be
(a) 2P
(b)
(c) P
(d) VIEW SOLUTION
- Question 2
- Question 3
If photons of frequency ν are incident on the surfaces of metals. A & B of threshold frequencies respectively, the ratio of the maximum kinetic energy of electrons emitted from A to that from B is
(a) 2 : 3
(b) 3 : 4
(c) 1 : 3
(d) VIEW SOLUTION
- Question 4
The electric flux through a closed Gaussian surface depends upon
(a) Net charge enclosed and permittivity of the medium
(b) Net, charge enclosed, permittivity of the medium and the size of the Gaussian surface
(c) Net charge enclosed only
(d) Permittivity of the medium only VIEW SOLUTION
- Question 5
A charge particle after being accelerated through a potential difference 'V' enters in a uniform magnetic field and moves in a circle of radius r. If V is doubled, the radius of the circle will become
(a) 2r
(b)
(c) 4r
(d) VIEW SOLUTION
- Question 6
The wavelength and intensity of light emitted by a LED depend upon
(a) forward bias and energy gap of the semiconductor
(b) energy gap of the semiconductor and reverse bias
(c) energy gap only
(d) forward bias only VIEW SOLUTION
- Question 7
The graph showing the correct variation of linear momentum (p) of a charge particle with its de-Broglie wavelength (λ) is -
VIEW SOLUTION
- Question 8
The selectivity of a series LCR a.c. circuit is large, when
(a) L is large and R is large
(b) L is small and R is small
(c) L is large and R is small
(d) L = R VIEW SOLUTION
- Question 9
Photo diodes are used to detect
(a) radio waves
(b) gamma rays
(c) IR rays
(d) optical signals VIEW SOLUTION
- Question 10
The relationship between Brewester angle 'θ' and the speed of light 'v' in the denser medium is –
(a) v tan θ = c
(b) c tan θ = v
(c) v sin θ = c
(d) c sin θ = v VIEW SOLUTION
- Question 11
The ability of a junction diode to __________ an alternating voltage, is based on the fact that it allows current to pass only when it is forward biased. VIEW SOLUTION
- Question 12
A point charge is placed at the centre of a hollow conducting sphere of internal radius 'r' and outer radius '2r'. The ratio of the surface charge density of the inner surface to that of the outer surface will be_________. VIEW SOLUTION
- Question 13
The ___________, a property of materials C, Si and Ge depends upon the energy gap between their conduction and valence bands. VIEW SOLUTION
- Question 14
A copper wire of non-uniform area of cross-section is connected to a d.c. battery. The physical quantity, which remains constant along the wire is __________. VIEW SOLUTION
- Question 15
The physical quantity having SI unit NC–1m is __________. VIEW SOLUTION
- Question 16
Depict the fields diagram of an electromagnetic wave propagating along positive X-axis with its electric field along Y-axis. VIEW SOLUTION
- Question 17
Write the conditions on path difference under which (i) constructive (ii) destructive interference occur in Young's double slit experiment. VIEW SOLUTION
- Question 18
Plot a graph showing variation of induced e.m.f. with the rate of change of current flowing through a coil.
OR
A series combination of an inductor (L), capacitor (C) and a resistor (R) is connected across an ac source of emf of peak value E0, and angular frequency (ω). Plot a graph to show variation of impedance of the circuit with angular frequency (ω). VIEW SOLUTION
- Question 19
Define the term 'current sensitivity' of a moving coil galvanometer. VIEW SOLUTION
- Question 20
An electron moves along +x direction. It enters into a region of uniform magnetic field. directed along –z direction as show in fig. Draw the shape of trajectory followed by the electron after entering the field.
OR
A square shaped current carrying loop MNOP is placed near a straight long current carrying wire AB as shown in the fig. The wire and the loop lie in the same plane. If the loop experiences a net force F towards the wire, find the magnitude of the force on the side 'NO' of the loop.
VIEW SOLUTION
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