Q1
short answer
2 marks
What is meant by energy band gap in a solid ? Draw the energy band diagrams for a conductor, an insulator and a semiconductor.
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Q2
short answer
2 marks
(a) 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.
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Q3
short answer
2 marks
OR (b) 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.
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Q3
short answer
2 marks
Name the device which converts electrical energy into light energy. Write three advantages of the device.
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Q5
short answer
(a) Differentiate between nuclear fission and nuclear fusion.
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Q5
short answer
3 marks
Answer the following, giving reason : (a) The resistance of a p-n junction in forward bias is low and in reverse bias is high. (b) For creating/making [semiconductors], doping is essential. (c) Photodiodes are operated in reverse bias.
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Q6
short answer
3 marks
(b) Deuterium undergoes fusion as per the reaction : H H He n 3·27 MeV1 0 3 2 2 1 2 1 Find the duration for which an electric bulb of 500 W can be kept glowing by the fusion of 100 g of deuterium.
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Q6
short answer
3 marks
(a) In Geiger-Marsden experiment, calculate the distance of closest approach for an alpha particle with energy 2·56 10^12 J. Consider that the particle approaches gold nucleus (Z = 79) in head-on position. (b) If the above experiment is repeated with a proton of the same energy, then what will be the value of the distance of closest approach ?
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Q7
short answer
3 marks
Briefly explain how bright and dark fringes are formed on the screen in fringe width.
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Q8
short answer
1 mark
The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased.
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Q8
long answer
3 marks
(a) (i) Draw a labelled ray diagram showing the formation of the image at infinity by an astronomical telescope. (ii) A telescope consists of an objective of focal length 150 cm and an eyepiece of focal length 6·0 cm. If the final image is formed at infinity, then calculate : (I) the length of the tube in this adjustment, and (II) the magnification produced.
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Q9
short answer
1 mark
Doping of intrinsic semiconductors is a necessity for making electronic devices.
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Q10
short answer
1 mark
Photodiodes are operated in reverse bias.
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Q11
short answer
3 marks
OR (b) 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.
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Q14
long answer
3 marks
(b) (i) Draw a labelled ray diagram showing the formation of the image at least distance of distinct vision by a compound microscope. (ii) A small object is placed at a distance of 3·0 cm from a magnifier of focal length 4·0 cm. Find : (I) the position of the image formed, and (II) the linear magnification produced.
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Q15
short answer
3 marks
Use Einstein photoelectric equation to depict the variation of the maximum kinetic energy (Ek) of electrons emitted, with the frequency (v) of the incident radiation.
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Q16
short answer
3 marks
A photosensitive surface is illuminated with a beam of (i) yellow light, and (ii) red light, both of the same intensity. In which case will (I) photoelectrons have more Ek ? (II) Justify your answer in each case.
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Q17
short answer
3 marks
(a) Identify the electromagnetic waves : (i) Which are used in radar systems. (ii) Which affect photographic plates. (iii) Which are used in surgery. Write their frequency range.
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Two transparent media of refractive indices n1 and n2 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 (R1 and R2) of its two surfaces and the refractive index (n) of the medium of the lens with respect to the surrounding medium. Depending on R1 and R2, 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.
Q20
mcq
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
- A. R1/n1 + R2/n2 = n1/u + n2/v
- B. R1/n2 + R2/n1 = n2/v - n1/u
- C. R1/n2 + R2/n1 = (n2 - n1)/v - (n2 - n1)/u
- D. R1/n1 + R2/n2 = (n2 - n1)/v - (n1 - n2)/u
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Q21
mcq
A point object is placed 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 :
- A. real and formed in glass.
- B. real and formed in air.
- C. virtual and formed in glass.
- D. virtual and formed in air
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Q22
mcq
An object is kept at 2F in front of an equiconvex lens. The image formed is :
- A. real and of the size of the object.
- B. virtual and of the size of the object.
- C. real and enlarged.
- D. virtual and diminished.
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Q23
mcq
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 :
- A. 5 D
- B. + 5 D
- C. + 15 D
- D. 15 D
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Q24
mcq
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 :
- A. f/4
- B. f/2
- C. f
- D. 2f
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Q310
short answer
3 marks
A ray of light is incident on a prism at an angle of 45 and passes symmetrically as shown in the figure. Calculate : (a) the angle of minimum deviation, (b) the refractive index of the material of the prism, and (c) the angle of refraction at the point P.
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