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ISC Class 12 Physics Solved Question Paper 2009

Short Answer Type

31. Give any two methods by which (ordinary) light can be polarised.

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32. A point source of monochromatic light ‘S’ is kept at the centre C of the bottom of a cylinder. Radius of the circular base of the cylinder is 15.0 cm. The cylinder contains water refractive index = 4/3 to a height of 7.0 cm.

Find the area of water surface through which light emerges in air.

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33.

An astronomical telescope consists of two convex lenses having focal length 80 cm and 4 cm. When it is in normal adjustment, what is its:

(i) Length,

(ii) Magnifying power?

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34. A convex lens of focal length 5 cm is to be used as a simple microscope. Where should an object be kept so that image formed by the lens lies at least distance D of distinct vision (D = 25 cm)? Also calculate the magnifying power of this instrument in this set up.

Focal length of convex lens = 5 cm

Position of image v = 25 cm

Position of object μ = ?

We know,

$1 over straight f space equals space 1 over v space minus space 1 over u T h a t space i s comma space 1 over straight f space equals space 1 over italic 25 space minus space 1 over u 1 over u space equals space 1 over italic 25 space minus space 1 fifth space equals space 4 over 25 straight u space equals space 25 over 4 space cm Magnifying space power space of space instrument colon straight M space equals space 1 space plus space straight D over straight f straight M space equals space 1 space plus space 25 over 5 space equals space 6$

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35. What are characteristic X rays? How are they different from continuous X rays? Give any one difference.

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36. Wavelength of the 1’st line (H_α) of Balmer series of hydrogen is 656.3 nm. Find the wavelength of its 2^nd line (H_β).

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37. Plot a labelled graph of [Vs] where Vs is stopping potential of photoelectrons versus frequency ‘f’ of incident radiation. How will you use this graph to determine the value of Planck’s constant? Explain

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38.

(i) Define ‘unified atomic mass unit’.

(ii) Find the minimum energy which a gamma ray photon should possess so that it is capable of producing an electron — positron pair.

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39. Fission of U - 235 nucleus releases 200 MeV of energy. Calculate the fission rate (i.e. no. of fissions per second) in order to produce a power of 320 MW.

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