Sound

31.	An empty earthen pitcher is kept under a water tap and starts filling with water as the tap is opened. The pitch of the sound produced
	A. goes on decreasing.
	B. goes on increasing.
	C. first increases and then decreases after the pitcher is half filled.
	D. does not change. Option “A” is correct. As the bottle fills up, the air column or amount of air inside the bottle decreases. So as a result, the pitch or shrillness of the sound will increase, as frequency or pitch of sound is inversely proportional to the length of vibrating air column. Also the amplitude or the loudness of the sound will decrease, as the amount of the air column vibrating decreases as the bottle fills up. So with the increase in shrillness of the sound, you can detect the filling up of the bottle. So the more the shrillness, the more the bottle has been filled. N.B. When the bottle overflows, the shrill sound will be heard no more

32.	Tuning of radio set is an example of __
	A. Reflection
	B. Resonance
	C. Interference
	D. Refraction Option “B” is correct. When the impedances or admittances of circuit elements cancel one another, electrical resonance occurs in an electric circuit at a specific resonant frequency. This occurs in some circuits when the transfer function is very close to one and the impedance between the circuit’s input and output is almost zero. Resonant circuits produce higher voltages or currents than are supplied into them and exhibit ringing. They are frequently employed for both transmission and reception in wireless (radio) transmission. When inductors and capacitors are used in a circuit, resonance happens because the inductor’s magnetic field collapses, creating an electric current in its windings that charges the capacitor, and the capacitor discharges, creating an electric current that strengthens the inductor’s magnetic field.

33.	When two loudspeakers are played simultaneously at a place, then the listener sitting at a particular place does not hear their sound, this is because
	A. Reflection
	B. Interference
	C. Refraction
	D. Resonance Option “B” is correct.

34.	Which one of the following is not produced by sound waves in air?
	A. Reflection
	B. Polarization
	C. Refraction
	D. Resonance Option”B” is correct

35.	When we sit inside the room, although we do not see the people talking in the next room, but we do hear their voices, this is because of the sound-
	A. Reflection
	B. Refraction
	C. Interference
	D. Diffraction Option “D” is correct. This is because sound waves undergo diffraction, bending and spreading as they go through the doorway between the two rooms.

36.	The Apparent change in the frequency of sound when the source, the observer and the medium are in a relative motion___
	A. Raman effect
	B. Doppler effect
	C. Crampton effect
	D. Photoelectric effect Option “B” is correct.

37.	Doppler effect is related to
	A. Sound
	B. Population
	C. Psychology
	D. Currency Circulation Option “A” is correct. The Apparent change in the frequency of sound when the source, the observer and the medium are in a relative motion is Doppler Effect.

38.	The frequency or sharpness of the whistle of the approaching train increases due to which phenomenon?
	A. Big bang theory
	B. Doppler effect
	C. Charles law
	D. Archimedes’ law Option “B” is correct. The correct option is the Doppler Effect. This phenomenon is explained by Doppler Effect which states that when there is a relative motion between the source and the observer of the sound, a variation in the frequency (pitch) of sound is observed by the observer. That’s why the frequency of a whistling train engine appears to increase when the train is approaching the platform.

39.	The speed of sound in moist air is more than that of dry air, because in moist air –
	A. Has a higher density than dry air
	B. Less dense than dry air
	C. Pressure is higher than that of dry air
	D. Less pressure than dry air Option “B” is correct. The lower the density, the faster sound travels in a medium. The density of water vapour is less than that of air. So the density of air mixed with water vapour is less than that of dry air. Hence the speed of sound in moist air is greater than that in dry air.

40.	Which one of the following statements is correct? Speed of sound
	A. Does not depend on the nature of the medium
	B. Maximum in gases and minimum in liquids
	C. Is maximum in solids and minimum in liquids
	D. Is maximum in solids and minimum in gases Option “D” is correct.

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