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Q:

When one enters a dark room after being in bright light one is not able to see anything clearly for a while because

A) the retina of the eye moves forward B) the retina of the eye moves backward
C) the iris is unable to dilate the pupil immediately to be able to see things D) the eye has no power of accommodation

Answer:   C) the iris is unable to dilate the pupil immediately to be able to see things



Explanation:

The size of the pupil of the eye automatically adjusts itself  according to the intensity of light passing through it;if the intensity is more , the size is less, if less, it is more. So in our case the pupil should dilate i.e, increase in size to be able to see in the dark . This switchover takes sometime. But here the entry into the dark room is immediate . So the eye has no time to adjust itself and hence is not able to see at all for a while.

Subject: Physics
Q:

If a carrier wave of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to _____ ?

A) 300 m B) 30 m
C) 3 m D) 0.3 m
 
Answer & Explanation Answer: A) 300 m

Explanation:

h =  straight c over straight v = 3 × 108/106 = 300 m

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Q:

Quality of transmission depends upon

A) Nature of signal only B) Nature of medium only
C) Both (A) and (B) D) Neither A nor B
 
Answer & Explanation Answer: C) Both (A) and (B)

Explanation:

Quality of transmission is governed both by nature of signal and nature of communication channel/medium.

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4 171
Q:

The rate of change of linear momentum of a body falling freely under gravity is equal to it's ____ ?

A) Kinetic Energy B) Weight
C) Potential Energy D) Impulse
 
Answer & Explanation Answer: B) Weight

Explanation:

Rate of change of impulse equals the force . In case of freely falling body the only force is the weight.

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Q:

A disk and a sphere of same radius but different masses roll on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ?

A) Depends on their masses B) Sphere
C) Disk D) Both reach at the same time
 
Answer & Explanation Answer: B) Sphere

Explanation:

Time does not depend on mass, else

  => is least for 'sphere' and

hence least time is taken by sphere.

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Q:

A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of the emf's is :

A) 3:4 B) 5:4
C) 5:1 D) 3:2
 
Answer & Explanation Answer: D) 3:2

Explanation:

In series : E1 + E2 = K(50)

In parallel : E1 - E2 = K(10)

E1 + E2 / E1 - E2 = 5/1

=> E1/E2 = 3/2

The emf's are in the ratio of 3:2.

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