CBSE Class 12 Physics 2022 question paper (55/4)

Maximum marks 35 · Time 2 hours · 3 sets

Try each question first, then open its model answer. Where the paper offers a choice, both questions are shown with OR between them.

Section A

2 marks each

Q.12 marks $What is meant by energy band gap in a solid ? Draw the energy band diagrams for a conductor, an insulator and a semiconductor.$
Q.2 (a)2 marks $Name the spectral series for a hydrogen atom which lies in the visible region. Find the ratio of the maximum to the minimum wavelengths of this series.$
OR
Q.2 (b)2 marks $What are matter waves ? A proton and an alpha particle are accelerated through the same potential difference. Find the ratio of the de Broglie wavelength associated with the proton to that with the alpha particle.$
Q.32 marks $Name the device which converts electrical energy into light energy. Write three advantages of the device.$

Section B

3 marks each

Q.43 marks ${}^{2}_{1}\mathrm{H} + {}^{2}_{1}\mathrm{H} \longrightarrow {}^{3}_{2}\mathrm{He} + {}^{1}_{0}\mathrm{n} + 3{\cdot}27\ \mathrm{MeV}$
Q.53 marks $Answer the following, giving reason : (a) The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased. (b) Doping of intrinsic semiconductors is a necessity for making electronic devices. (c) Photodiodes are operated in reverse bias.$
Q.63 marks $2{\cdot}56 \times 10^{-12}$
Q.73 marks $Briefly explain how bright and dark fringes are formed on the screen in Young's double slit experiment. Hence, derive the expression for the fringe width.$
Q.8 (a)3 marks $6{\cdot}0$
OR
Q.8 (b)3 marks $3{\cdot}0$
Q.93 marks $(\mathrm{E_k})$
Q.103 marks $45^\circ$
Q.11 (a)3 marks $Identify electromagnetic waves which : (i) are used in radar system. (ii) affect a photographic plate. (iii) are used in surgery. Write their frequency range.$
OR
Q.11 (b)3 marks $A plane wavefront is propagating from a rarer into a denser medium. Use Huygens principle to show the refracted wavefront and verify Snell's law.$

Section C

1 mark each

Two transparent media of refractive indices $\mathrm{n_1}$ and $\mathrm{n_2}$ are separated by a spherical transparent surface. The rays of light incident on the surface get refracted into the medium on the other side. The laws of refraction are valid at each point of the spherical surface. A lens is a transparent optical medium bounded by two surfaces, at least one of which should be spherical. The focal length of a lens is determined by the radii of curvature $(\mathrm{R_1}$ and $\mathrm{R_2})$ of its two surfaces and the refractive index (n) of the medium of the lens with respect to the surrounding medium. Depending on $\mathrm{R_1}$ and $\mathrm{R_2}$ , a lens behaves as a diverging or a converging lens. The ability of a lens to diverge or converge a beam of light incident on it defines its power.
Q.12 (a)1 mark $An object is placed at the point B as shown in the figure. The object distance (u) and the image distance (v) are related as$
Tap an option to check your answer.
Q.12 (b)1 mark $A point object is placed in air at a distance 'R' in front of a convex spherical refracting surface of radius of curvature R. If the medium on the other side of the surface is glass, then the image is :$
Tap an option to check your answer.
Q.12 (c)1 mark $An object is kept at 2F in front of an equiconvex lens. The image formed is :$
Tap an option to check your answer.
Q.12 (d)1 mark $A thin converging lens of focal length 10 cm and a thin diverging lens of focal length 20 cm are placed coaxially in contact. The power of the combination is :$
Tap an option to check your answer.
Q.12 (e)1 mark $An equiconcave lens of focal length 'f' is cut into two identical parts along the dotted line as shown in the figure. The focal length of each part will be :$
Tap an option to check your answer.

Section A

2 marks each

Q.12 marks $What is meant by energy band gap in a solid ? Draw the energy band diagrams for a conductor, an insulator and a semiconductor.$
Q.22 marks $Name the device which converts an ac input signal into a dc output signal. Write the principle of working of the device.$
Q.3 (a)2 marks $Name the spectral series for a hydrogen atom which lies in the visible region. Find the ratio of the maximum to the minimum wavelengths of this series.$
OR
Q.3 (b)2 marks $What are matter waves ? A proton and an alpha particle are accelerated through the same potential difference. Find the ratio of the de Broglie wavelength associated with the proton to that with the alpha particle.$

Section B

3 marks each

Q.43 marks ${}^{2}_{1}\mathrm{H} + {}^{2}_{1}\mathrm{H} \longrightarrow {}^{3}_{2}\mathrm{He} + {}^{1}_{0}\mathrm{n} + 3{\cdot}27\ \mathrm{MeV}$
Q.53 marks $2{\cdot}56 \times 10^{-12}$
Q.63 marks $Answer the following, giving reason : (a) The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased. (b) Doping of intrinsic semiconductors is a necessity for making electronic devices. (c) Photodiodes are operated in reverse bias.$
Q.73 marks $\mathrm{S_1}$
Q.83 marks $\lambda$
Q.9 (a)3 marks $6{\cdot}0$
OR
Q.9 (b)3 marks $3{\cdot}0$
Q.10 (a)3 marks $Identify electromagnetic waves which : (i) are used in radar system. (ii) affect a photographic plate. (iii) are used in surgery. Write their frequency range.$
OR
Q.10 (b)3 marks $A plane wavefront is propagating from a rarer into a denser medium. Use Huygens principle to show the refracted wavefront and verify Snell's law.$
Q.113 marks $\textcircled{1}$

Section C

1 mark each

Two transparent media of refractive indices $\mathrm{n_1}$ and $\mathrm{n_2}$ are separated by a spherical transparent surface. The rays of light incident on the surface get refracted into the medium on the other side. The laws of refraction are valid at each point of the spherical surface. A lens is a transparent optical medium bounded by two surfaces, at least one of which should be spherical. The focal length of a lens is determined by the radii of curvature $(\mathrm{R_1}$ and $\mathrm{R_2})$ of its two surfaces and the refractive index (n) of the medium of the lens with respect to the surrounding medium. Depending on $\mathrm{R_1}$ and $\mathrm{R_2}$ , a lens behaves as a diverging or a converging lens. The ability of a lens to diverge or converge a beam of light incident on it defines its power.
Q.12 (a)1 mark $An object is placed at the point B as shown in the figure. The object distance (u) and the image distance (v) are related as$
Tap an option to check your answer.
Q.12 (b)1 mark $A point object is placed in air at a distance 'R' in front of a convex spherical refracting surface of radius of curvature R. If the medium on the other side of the surface is glass, then the image is :$
Tap an option to check your answer.
Q.12 (c)1 mark $An object is kept at 2F in front of an equiconvex lens. The image formed is :$
Tap an option to check your answer.
Q.12 (d)1 mark $A thin converging lens of focal length 10 cm and a thin diverging lens of focal length 20 cm are placed coaxially in contact. The power of the combination is :$
Tap an option to check your answer.
Q.12 (e)1 mark $An equiconcave lens of focal length 'f' is cut into two identical parts along the dotted line as shown in the figure. The focal length of each part will be :$
Tap an option to check your answer.

Section A

2 marks each

Q.1 (a)2 marks $Name the spectral series for a hydrogen atom which lies in the visible region. Find the ratio of the maximum to the minimum wavelengths of this series.$
OR
Q.1 (b)2 marks $What are matter waves ? A proton and an alpha particle are accelerated through the same potential difference. Find the ratio of the de Broglie wavelength associated with the proton to that with the alpha particle.$
Q.22 marks $What is meant by energy band gap in a solid ? Draw the energy band diagrams for a conductor, an insulator and a semiconductor.$
Q.32 marks $Define barrier potential. Why does the thickness of the depletion layer in a p-n junction diode vary with increase in reverse bias ?$

Section B

3 marks each

Q.43 marks $Answer the following, giving reason : (a) The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased. (b) Doping of intrinsic semiconductors is a necessity for making electronic devices. (c) Photodiodes are operated in reverse bias.$
Q.53 marks ${}^{2}_{1}\mathrm{H} + {}^{2}_{1}\mathrm{H} \longrightarrow {}^{3}_{2}\mathrm{He} + {}^{1}_{0}\mathrm{n} + 3{\cdot}27\ \mathrm{MeV}$
Q.63 marks $Briefly explain how bright and dark fringes are formed on a screen due to the diffraction at a single slit. Hence, explain why the intensity at the bright fringes decreases sharply as their order (n) increases.$
Q.7 (a)3 marks $6{\cdot}0$
OR
Q.7 (b)3 marks $3{\cdot}0$
Q.83 marks $\lambda$
Q.93 marks $2{\cdot}56 \times 10^{-12}$
Q.10 (a)3 marks $Identify electromagnetic waves which : (i) are used in radar system. (ii) affect a photographic plate. (iii) are used in surgery. Write their frequency range.$
OR
Q.10 (b)3 marks $A plane wavefront is propagating from a rarer into a denser medium. Use Huygens principle to show the refracted wavefront and verify Snell's law.$
Q.113 marks $\left(\mu = \frac{4}{3}\right)$

Section C

1 mark each

Two transparent media of refractive indices $\mathrm{n_1}$ and $\mathrm{n_2}$ are separated by a spherical transparent surface. The rays of light incident on the surface get refracted into the medium on the other side. The laws of refraction are valid at each point of the spherical surface. A lens is a transparent optical medium bounded by two surfaces, at least one of which should be spherical. The focal length of a lens is determined by the radii of curvature $(\mathrm{R_1}$ and $\mathrm{R_2})$ of its two surfaces and the refractive index (n) of the medium of the lens with respect to the surrounding medium. Depending on $\mathrm{R_1}$ and $\mathrm{R_2}$ , a lens behaves as a diverging or a converging lens. The ability of a lens to diverge or converge a beam of light incident on it defines its power.
Q.12 (a)1 mark $An object is placed at the point B as shown in the figure. The object distance (u) and the image distance (v) are related as$
Tap an option to check your answer.
Q.12 (b)1 mark $A point object is placed in air at a distance 'R' in front of a convex spherical refracting surface of radius of curvature R. If the medium on the other side of the surface is glass, then the image is :$
Tap an option to check your answer.
Q.12 (c)1 mark $An object is kept at 2F in front of an equiconvex lens. The image formed is :$
Tap an option to check your answer.
Q.12 (d)1 mark $A thin converging lens of focal length 10 cm and a thin diverging lens of focal length 20 cm are placed coaxially in contact. The power of the combination is :$
Tap an option to check your answer.
Q.12 (e)1 mark $An equiconcave lens of focal length 'f' is cut into two identical parts along the dotted line as shown in the figure. The focal length of each part will be :$
Tap an option to check your answer.