10.5 RIPPLE TANK
Ripple tank is a device to produce water waves and to study their characteristics.
This apparatus consists of a rectangular tray having glass bottom and is placed nearly half metre above the surface of a table (Fig. 10.11). Waves can be produced on the surface of water present in the tray by means of a vibrator (paddle).
This vibrator is an oscillating electric motor fixed on a wooden plate over the tray such that its lower surface just touches the surface of water. On setting the vibrator ON, this wooden plate starts vibrating to generate water waves consisting of straight wavefronts (Fig.10.12). An electric bulb is hung above the tray to observe the image of water waves on the paper or screen. The crests and troughs of the waves appear as bright and dark lines respectively, on the screen. Now we explain the reflection of water waves with the help of ripple tank.
Place a barrier in the ripple tank. The water waves will reflect from the barrier. If the barrier is placed at an angle to the wavefront, the reflected waves can be seen to obey the law of reflection i.e., the angle of the incident wave along the normal will be equal to the angle of the reflected wave (Fig.10.13). Thus, we define reflection of waves as:
When waves moving in one medium fall on the surface of another medium they bounce back into the first medium such that the angle of incidence is equal to the angle of reflection.