Q13 of 50 Page 12

Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen. Why?

This happens because of the difference in the velocity of light and sound waves. Light travels with much faster velocity than sound. That’s why thunder is heard a few seconds after the flash of thunder is seen instead of both are produced simultaneously.

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11

An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s-1?

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Two children are at opposite ends of an aluminium rod. One strikes the end of rod with a stone. Find the ratio of times taken by sound wave in air and in aluminium to reach the second child (Given: Speed of sound in air = 346 m/s; Speed of sound in aluminium = 6240 m/s)

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What type of wave is represented :

(a) by density-distance graph?


(b) by displacement-distance graph?

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State the general name of the waves on which the particles of the medium vibrate:

(i) in the same direction as wave.


(ii) at right angles to the direction of wave.