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ISC Class 12 Physics Solved Question Paper 2004

Short Answer Type

31. Draw the circuit diagram for a common emitter NPN transistor, stating the input and output wave form.

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32. What are logic gates. Give the electronic circuit for the realization of AND GATE. [Diode combination showing input and output with biasing].

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Long Answer Type

33. State and prove Tangent law.

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34. A magnet makes 12 oscillations per minute in the earth’s magnetic field alone and 15 oscillations per minute when a short magnet with its axis horizontal and its south pole pointing north is placed with its center 20 cm directly above the oscillating magnet. Find the magnetic moment of the magnet. (Given : B_H= 0.36 x 10^-4 Tesla).

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35. What is meant by back e.m.f. of a motor ? The back e.m.f. of a motor delivering 5 kW is 100 V, while operating on 110 V supply. Find the current and resistance of the motor.

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36. What are the conditions necessary for sustained interference?

In Young’s double slit experiment the distance of the 4th Bright fringe from the central zero is 1.5 mm. The distance between the slits and the screen is 1.5 m and the distance between the slits is 2 mm. Find the wavelength of light used.

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37. State one experiment to determine the velocity of light. Draw necessary ray diagram and derive the formula used.

i) The source of light S passing through a slit is rendered parallel by an achromatic lens L and is incident on the face of an octagonal mirror M_l at an angle of 45°.

ii) It is then reflected to a distance by a concave mirror, after travelling a distance x.

iii) This light, is then is reflected by a concave mirror M₃ and by a fixed plane mirror M₂.

iv) After reflection from M₂, it returns and is incident on another face of the mirror M₁ and is received by the eye-piece of a telescope T, as shown in the diagram.

v) At the mirror M₁ rotates, in a clockwise direction, the returning rays into the reflected face of the mirror and image in T will be displaced.

vi) The speed of the mirror is to adjusted that the face of the mirror just occupies the position of the next face in the time the light takes in travelling fromM₁ to M₂ and back.

vii) Then the image in T will be found in the same plane, where it was when M_l was at rest.

viii) If at this time, n be the frequency of revolution per second. The time to return through l/8th of a revolution is l/8n seconds.

ix) If the distance travelled by light in its path from M_l to M₂ be d, the time taken by the light in the double journey is 2d/c where, c is the velocity of light.

Hence,

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38.

Derive the formula for angular magnification of a compound microscope, when the final image is formed at least distance of distinct vision. Draw the required ray diagram.

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39.

Give the expression for the velocity of electron in the first orbit of Hydrogen atom and for the radius in the ground state of Hydrogen atom.

Hence derive the expression for the kinetic energy of the electron.

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40.

In Millikan’s oil drop experiment, a charged oil drop of density 880 kg/m³ is held stationary between two parallel plates 6.0 mm apart at a potential difference of 1000 volts. When electric field E is switched off, the oil drop was observed to fall a distance of 2.0 mm in 35.7 seconds. [4]

(i) Find the radius of oil drop.

Given :

η for air = 1.8 x 10^-5 poise

Density of air = 1.29 kg/m³

Use g = 9.81 m/s²

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