CBSE 12th Physics Question Paper 2022 (Set 2) with Answers

CBSE 12th Physics Question Paper 2022 (Set 2)

28 questions from this Grade 12 Physics paper. The first 5 questions are solved free; log in as a Grade 12 student to view all solutions.

Q1 short answer 2 marks

(a) (i) Define impact parameter and distance of closest approach for an alpha-particle in Geiger-Marsden scattering experiment. (ii) What will be the value of the impact parameter for scattering angle (I) = 0 and (II) = 180?

Solution

(i) Impact parameter (b) is the perpendicular distance of the initial velocity vector of the alpha-particle from the center of the nucleus. Distance of closest approach (r0) is the distance of the alpha-particle from the nucleus at the moment it comes to momentary rest before reversing its direction. (ii) For scattering angle theta = 0, b = infinity (or maximum possible). For theta = 180 degrees, b = 0 (head-on collision).

Q2 short answer 2 marks

Photoelectric emission occurs when a surface is irradiated with the radiation of frequency (i) v1, and (ii) v2. The maximum kinetic energy of the electrons emitted in the two cases are K and 2K respectively. Obtain the expression for the threshold frequency for the surface.

Solution

According to Einstein's photoelectric equation, K = hv - hv0. For frequency v1: K = hv1 - hv0 (1). For frequency v2: 2K = hv2 - hv0 (2). Multiplying (1) by 2: 2K = 2hv1 - 2hv0 (3). Equating (2) and (3): hv2 - hv0 = 2hv1 - 2hv0. This gives hv0 = 2hv1 - hv2. Thus, the threshold frequency v0 = (2v1 - v2).

Q2 short answer 2 marks

Briefly explain the working of a light emitting diode. Mention its two uses.

Solution

A Light Emitting Diode (LED) is a heavily doped p-n junction that emits spontaneous radiation when forward-biased. When forward-biased, electrons from the n-region and holes from the p-region move toward the junction and recombine. This recombination of charge carriers releases energy in the form of photons. Uses: (1) In optical communication and (2) In display panels (TVs, smartphones, etc.).

Q3 short answer 2 marks

Explain the formation of depletion region in a p-n junction.

Solution

When a p-n junction is formed, the difference in carrier concentration leads to the diffusion of holes from the p-side to the n-side and electrons from the n-side to the p-side. This diffusion leaves behind uncompensated ionized acceptors in the p-region and ionized donors in the n-region near the junction. This space charge region, which is devoid of free mobile charge carriers, is called the depletion region.

Q4 long answer 3 marks

With the help of a circuit diagram, explain the working of a p-n junction diode as a full-wave rectifier. Also draw its input and output waveforms.

Solution

A full-wave rectifier uses two diodes. During the first half of the AC cycle, one diode is forward-biased and conducts; during the second half, the other diode is forward-biased. The current through the load resistance flows in the same direction for both halves. [Circuit Diagram: Two diodes D1 and D2 connected to a center-tapped transformer with load RL]. The input waveform is a continuous sine wave, while the output waveform consists of positive half-cycles for both the positive and negative input cycles.

Q5 long answer 3 marks

Find the ratio of the de Broglie wavelengths associated with an alpha particle and a proton, if both (a) have the same speeds, (b) have the same kinetic energy, (c) are accelerated through the same potential difference.

Solution hidden

Q6 short answer

What is the -particle in Geiger-Marsden scattering experiment?

Solution hidden

Q7 short answer 2 marks

What will be the value of the impact parameter for scattering angle (I) = 0 and (II) = 180 ?

Solution hidden

Q9 long answer

Depict the variation of the potential energy of a pair of nucleons with the separation between them.

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Q10 long answer 3 marks

Imagine the fission of a Fe 56/26 into two equal fragments of Al 28/13 nucleus. Is the fission energetically possible ? Justify your answer by working out Q value of the process. Given : m Fe 56/26 = 55.93494 u, m Al 28/13 = 27.98191 u.

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Q10 long answer 3 marks

A small bulb is placed at the bottom of a tank filled with water to a depth of 70 cm. Find the surface area of the water through which the light of the bulb can emerge. The refractive index of water is 4/3.

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Q11 long answer

Depict a plane electromagnetic wave propagating along the x-axis. Write the expressions for its oscillating electric and magnetic fields.

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Q11 long answer 3 marks

The refractive index of an equilateral triangular prism is sqrt(2). Calculate (a) minimum angle of deviation (b) critical angle for the prism.

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Q12 long answer 3 marks

Write three characteristics of electromagnetic waves.

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Q13 long answer 3 marks

Name the electromagnetic waves which are produced by the following : (i) Radioactive decays of nucleus (ii) Welding arcs (iii) Hot bodies. Write one use each of these waves.

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Q14 long answer 3 marks

Draw a labelled ray diagram showing the formation of an image by an astronomical refracting telescope in normal adjustment. Hence, obtain the expression for its magnifying power.

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Q15 long answer 3 marks

Light of wavelength is incident normally on a slit. (i) Depict the intensity distribution in the pattern observed. (ii) Obtain the expression for the first maximum from the central maximum.

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Q16 long answer 3 marks

Use the energy level diagram shown below to obtain the relation between three wavelengths 1, 2 and 3 emitted due to the transition of electron from the energy states C and B.

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Reading Passage

English physicist Thomas Young explained the interference of light using the principle of superposition of waves. He observed the interference pattern on a screen through his experimental arrangement, now called Young's double-slit experiment. He illuminated two slits S1 and S2 with light coming from a slit S. This interference pattern is made of bright and dark bands. These types of bands are called fringes. The distance between two consecutive bright and dark fringes is called fringe width.

Q19 mcq

If the screen is moved towards the slits S1 and S2, the fringe width: (i) decreases, but intensity of bright fringe remains the same (ii) increases, but intensity of bright fringe decreases (iii) decreases, and intensity of bright fringe decreases (iv) and intensity both remain the same.

A. decreases, but intensity of bright fringe remains the same
B. increases, but intensity of bright fringe decreases
C. decreases, and intensity of bright fringe decreases
D. and intensity both remain the same

Solution hidden

Q20 mcq

When both slits S1 and S2 are replaced by two independent but identical sources: (i) the pattern will remain unchanged (ii) pattern intensity will decrease (iii) fringes will disappear (iv) intensity will increase

A. the pattern will remain unchanged
B. pattern intensity will decrease
C. fringes will disappear
D. intensity will increase

Solution hidden

Q21 short answer

Is the speed of light in glass independent of the colour of light ? Give reason.

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Q22 short answer 3 marks

The refractive index of an equilateral triangular prism kept in air is root 2. Calculate: (a) the angle of minimum deviation.

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Q23 short answer

The refractive index of an equilateral triangular prism kept in air is root 2. Calculate: (b) the critical angle for the prism.

Solution hidden

Reading Passage

The British physicist Thomas Young explained the interference of light using the principle of superposition of waves. He observed the interference pattern on the screen, in his experimental set-up, known as Young's double slit experiment. The two slits S1 and S2 were illuminated by light from a slit S. The interference pattern consists of dark and bright bands of light. Such bands are called fringes. The distance between two consecutive bright and dark fringes is called fringe width.

Q24 mcq 1 mark

If the screen is moved closer to the plane of slits S1 and S2, then the fringe width :

A. will decrease, but the intensity of bright fringe remains the same.
B. will increase, but the intensity of bright fringe decreases.
C. will decrease, but the intensity of bright fringe increases.
D. and the intensity both remain the same.

Solution hidden

Q25 mcq 1 mark

What will happen to the pattern on the screen, when the two slits S1 and S2 are replaced by two independent but identical sources ?

A. The intensity of pattern will increase
B. The intensity of pattern will decrease
C. The number of fringes will become double
D. No pattern will be observed on the screen

Solution hidden

Q26 mcq 1 mark

Two sources of light are said to be coherent, when both emit light waves of :

A. same amplitude and have a varying phase difference.
B. same wavelength and a constant phase difference.
C. different wavelengths and same intensity.
D. different wavelengths and a constant phase difference.

Solution hidden

Q27 mcq 1 mark

The fringe width is beta. If the whole set-up is immersed in a liquid of refractive index n, then the new fringe width will be :

A. beta/n
B. beta * n
C. beta
D. 2 * beta

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Q28 mcq 1 mark

The total path difference between two waves meeting at points P1 and P2 on the screen are lambda/3 and 2 lambda respectively. Then :

A. bright fringes are formed at both points.
B. dark fringes are formed at both points.
C. a bright fringe is formed at P1 and a dark fringe is formed at P2.
D. a bright fringe is formed at P2 and a dark fringe is formed at P1.

Solution hidden