Q4 of 33 Page 174

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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2

Why is sound wave called a longitudinal wave?

 3

Which characteristic of the sound helped you to identify your friend by his voice while sitting with others in a dark room?

 5

A person has a hearing range from 20 kHz. What is the typical wavelength of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 m s-1?

 6

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)