question_answer

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 the spring sideways. (ii) Waves produced in a cylinder containing a liquid by moving its piston back and forth. (iii) Waves produced by a motor boat sailing in water. (iv) Light waves travelling from the sun to the earth. (v) Ultrasonic waves in air produced by a vibrating quartz crystal.          

Answer:

                (i) Transverse wave motion, because the vibrations of particles (kinks) of the spring are at right angles to the direction of wave propagation. (ii) Longitudinal wave motion, because the molecules of the liquid vibrate to and fro about their mean position along the direction of propagation of the wave. (iii) Combination of longitudinal and transverse waves, because the propeller of the molar boat cuts the water surface laterally and also pushes it in backward direction. (iv) Transverse wave motion, because the light waves are electromagnetic waves in which electric and magnetic fields vibrate in the direction at right angle to each other and also to the direction of propagation of the wave. (v) Ultrasonic waves produced by a quartz crystal in air are longitudinal because the molecules of air vibrate to and fro about their mean positions along the direction of propagation of wave due to vibrations of quartz crystal.