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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.

The voltage that exists in electric motors, where there is a relative motion between the armature of the motor and the magnetic field from the motor's field magnets.

Suppose motor e.m.f. of motor increases with increase in speed of the armature of coil.

i.e., I =

fraction numerator straight E space minus space straight V over denominator straight R end fraction space space space space space space space space space space space space space space space space space space space space space... space left parenthesis 1 right parenthesis thin space

where,

E = applied e.m.f. = 110 V

V = back e.m.f. = 100 V

R = resistance of armature and

I = current

We have,

Mechanical power, P = EI-I²R = VI

or EI-I²R = VI ...(2)

Putting the value E and V_in eqn. (2), we get

⇒ 110I-I²R = 100xI

or 100 -IR = 100

IR = 110- 100= 10

We know that,

P = VI ...(3)

where

P = 5 KW = 5 x 10³ W

⇒ 100 x I = 5 x 10³or I = $5000 over 100 space equals space 50 space A$

Also we know that,

V = IR

$straight R space equals space straight V over straight I space equals space 10 over 50 space equals space 0.2 space straight capital omega$

Hence,

Current I = 50 A and

Resistance (R) = 0.2 Ω

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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.

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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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