SCIENTIFIC REASONING QUESTIONS FOR ALL COMPETITIVE EXAMS

61) Why is cooking quicker in a pressure cooker?

Ans: The boiling point of water depends upon the pressure on its surface. Steam produced inside the

cooker builds up pressure thereby raising the boiling point of water, which results in quick cooking.

62) Why does steam cause more severe burns than boiling water?

Ans: The amount of heat (latent heat) possessed by steam is much greater than the amount of heat

possessed by water at the same temperature. Therefore, steam causes more severe burns than boiling water.

63) Why does ice not melt readily when salt is sprinkled over it?

Ans: When salt is sprinkled over ice, some of it dissolves. As dissolution of the salt is accompanied

by absorption oh heat. The temperature of the system falls below 0 degree Celsius. Hence, ice does

not melt readily.

64) It is difficult for firemen to hold a hose, which ejects large amount of water at a high velocity.

Why?

Ans: the water which comes out of the fireman‘s hose carries large momentum as its velocity is very

high. The equal and opposite reaction force pushes the fireman backwards with a great speed

satisfying the law of conservation of momentum. As a result, it is difficult for the fireman to hold the

hose.

65) In the outer space astronauts talk to each other through radios. Why?

Ans: sound waves need a material medium for its propagation. There is no air in space and hence,

sound waves cannot travel. However, radio waves can travel through space. The astronauts can see

each other because light, like radio waves, can travel through vacuum.

66) Sonar scanners are used by doctors. Explain.

Ans: sonar scanners send out ultrasonic waves, which are reflected by body tissue and organs. From

the pattern of reflections, a computer can build up an image of the internal structure which is vital for

diagnosis.

67) Why the flash of lightning is seen before the sound of thunder is heard?

Ans: the velocity of light is much greater than that of the sound. Therefore, flash of lightning is seen

before the sound of thunder is heard.

68) Bats have poor eyesight but are able to home their prey with great accuracy. Also, dolphins can

avoid fishing nets and can detect fish at night. Explain

Ans: Bats emit high frequency (1, 20,000 Hz) sound waves and listen with their sensitive ears for any

echoes. From the time taken to hear the echo and from the nature of sound received. Bats are able to

estimate the distance and the type of surroundings. This process is known as echolocation. Same

process is used by the dolphins.

69) When low flying aircraft passes overhead, we sometimes notice a slight disturbance on our TV

screen. Why is it so?

Ans: a low flying aircraft reflects TV signal. Due to the interference between the direct signal and the

reflected signal, there is disturbance on the TV screen.

70) In automobiles, why are convex mirrors used to see the traffic from behind?

Ans: Convex mirrors are used in automobiles because they form erect and diminished images of the

object. Thus, it helps the drivers to get a wider field of view of the traffic coming from behind.