Physics - Study Mode

[#971] Woollen cloth protects the body from cold because
Correct Answer

(B) It is a poor conductor of heat

Explanation

Solution: Cotton clothes are thin and do not have space in which air can be trapped. Thus, cotton clothes do not prevent heat coming out of our body. Woollen clothes keep us warm during winter because wool is a poor conductor of heat and it has air trapped in between the fibres.

[#972] Hot water is poured simultaneously in four metallic tumblers painted outside with different paints. After some time the water will be found to have cooled most in the tumbler painted.
Correct Answer

(B) Rough black

Explanation

Solution: Hot water is poured simultaneously in four metallic tumblers painted outside with different paints. After some time the water will be found to have cooled most in the tumbler painted rough black. Black surfaces are good emitters of heat.

[#973] The intensity ratio of waves is 25 : 9. What is the ratio of their amplitudes?
Correct Answer

(D) 5 : 3

Explanation

Solution: In general, the intensity of a wave is proportional to the square of its amplitude. This has an important implication: relative intensity can be obtained by squaring relative amplitude. I α a 2 So if the intensity ratio is 25:9, the amplitude ratio will be 5:3.

[#974] The velocity of sound in air
Correct Answer

(D) Decreases with decrease of temperature

Explanation

Solution: The velocity of sound in air decreases with decrease of temperature.

[#975] Infrasonic sound has a frequency lower than
Correct Answer

(C) 20 Hz

Explanation

Solution: Infrasonic Sound has a frequency less than the audible frequency range. Frequencies are less than 20 Hz. The infrasonic sounds have below the lower limit of human hearing.