State two properties of the medium on which the speed of sound in it depends.

The sound of an explosion on the surface of a lake is heard by a boat man 100 m away and by a diver 100 m below the point of explosion.

(i) Who would hear the sound first — boat man or diver?
(ii) Give a reason for your answer in part (i)
(iii) If sound takes time t to reach the boat man, how much time approximately does it take to reach the diver?

Draw a displacement-distance graph of a wave and mark on it, the amplitude of wave by the letter a and wavelength of wave by the letter λ.

If you place your ear close to an iron railing which is struck some distance away, you hear the sound twice. Explain why?