Question # 1

Ultra-violet radiation of 6.2 eV falls on an aluminium surface. K.E. of fastest electron emitted is (Work function = 4.2 eV)

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3.2 x 10-21 J

3.2 x 10-19 J

7 x 10-25 J

9 x 10-32 J

Steel is preferred for making springs over copper. Why?

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Steel is cheaper

Young's modulus of steel is more than that of copper

Young's modulus of copper is more than that of steel

Steel is less likely ot be oxidized

If the period of oscillation of mass (M) suspended from a spring is 2s, then the period of mass 4M will be

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1 s

2 s

3 s

4 s

If the amplitude of sound is doubled and the frequency reduced to one-fourth, the intensity of sound at the same point will be

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Increasing by a factor of 2

Decreasing by a factor of 2

Decreasing by a factor of 4

Unchanged

If the earth were to rotate faster, than its present speed the weight of an object will

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Increase at the equator but remain unchanged at the poles

Decrease at the equator but remain unchanged at the poles

Remain unchanged at the decrease but decrease at the poles

Remain unchanged at the equator but increase at the poles

In a common base transistor circuit, the current gain is 0.98. On changing the emitter current by 5.00 mA, the change in collector current is

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0.916 mA

2.45 mA

4.9 mA

5.1 mA

When a hydrogen atom is bombarded, the atom is excited to the n = 4 state of hydrogen atom. The energy released when the atom falls from n = 4 state to the ground state is

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1.275 eV

12.75 eV

5 eV

8 eV

A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen

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Half the image will disappear

No change either in size or in intensity

Intensity of image will increase

Intensity of the image will decrease

A fly is sitting on the objective of a telescope pointed towards the moon.

What effect is expected on the photography of the moon taken through the telescope?

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The entire of view blocked

There is an image of the fly on the photography

There is no effect at all

There is a reduction in the intensity of the image

Copper and germanium are cooled to 70K from room temperature, then

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Resistance of copper increases while that of germanium decreases

Resistance of copper decreases while that of germanium increases

Resistance of both decreases

Resistance of both increases

A 220 V, 50 Hz. A.C. source is connected to an inductance of 0.2 H and a resistance of 20 ohm in series. What is the current in the circuit?

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10 A

5 A

33.3 A

3.33 A

A conducting wire is drawn to double its length. Final resistivity of the material will be

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Double of the original one

Half of the original one

One-fourth of the original one

Same as original one

The part of a transistor which is heavily doped to produce large number of majority carriers is

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Emitter

Base

Collector

Any of the above depending on nature of transistor

A monochromatic source of light is placed at a large distance d from a metal surface. Photoelectrons are ejected at rate n, kinetic energy being E. If the source is brought nearer to distance d/2, the rate and kinetic energy per photoelectron become nearly

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2n and 2E

4n and 4E

4n and E

N and 4E

A boy is dropped from a tower with zero velocity, reaches ground in 4s. The height of the tower is about

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80 m

20 m

160 m

40 m

The temperature at which the speed of sound becomes double as was at 27°C is

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273°C

0°C

927°C

1027°C

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