﻿ Plot a labelled graph of [Vs] where Vs is stopping potential of

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## ISC Class 12 Physics Solved Question Paper 2009

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.
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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 (Hα) of Balmer series of hydrogen is 656.3 nm. Find the wavelength of its 2nd line (Hβ).
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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

Graph of [VS](Stopping potential) versus frequency f.

This graph is drawn by taking frequency along X-axis and stopping potential along Y-axis as shown in fig.

At starting it is a straight line. The X-intercept gives the threshold frequency v
0. So there is no photoelectric emission. Slope of the graph = h/e.

We can find the slope of graph easily.

The value can also be found from the graph.

In this graph, e = b -a

Therefore, by finding the value of e and slope of graph we can find the Plank’s constant K.

Plank’s constant, K = Slope of graph x e

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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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40.  Draw a neatly labelled circuit diagram of a Full Wave rectifier using two juction diodes.
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