What type of wave is represented :

(a) by density-distance graph?

(b) by displacement-distance graph?

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)

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

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.

What is sonar? Explain its use.