Given below are some examples of wave motion. State in each case, if the wave motion is transverse, longitudinal or a combination of both?
(i) Motion of a kink in a long coil spring produced by displacing one end of spring side ways.
(ii) Waves produed in a cylinder containing a liquid by moving its piston back and forth.
(iii) Waves produed by a motor boat sailing in water.
(iv) Light waves travelling from sun to earth.
(v) ultrasonic waves in air produced by a vibrating quartz crystal.

Explanation

(a) In this case, vibrations of the particles (kinks) of the spring are at right angles to the direction of wave propagation. So, the wave motion is transverse in nature.
(b) In this case, molecules of the liquid vibrate to and fro about their mean position along the direction of propagation of the wave. So, the wave motion is longitudinal in nature.
(c) In this case, the propeller of the motor boat draws the water back. So, a longitudinal wave is generated. Also, it goes laterally deep into the water, generating transverse wave. So, the wave motion is both transverse and longitudinal in nature.
(d) In this case, the molecules of air vibrate to and fro from their mean positions along the direction of propagation of wave due to vibration of the quartz crystal. So, the wave motionn is longitudinal in nature.