Refraction occurs when waves travel from deeper to shallow water regions and vice versa.
-In ripple tank, a shallow region is created by placing a transparent plate at one end of the tank with its edge parallel to the vibrating bar.
- The separation of waves at deeper and shallowregions is noted.
- The experiment is repeated with the glass at an  angle to the waves.

From deep to shallow region, the separation becomes smaller as shown.
The separation is equivalent to the wavelength.

Wave from deep to shallow at an angle

EXPLANATION ON REFRACTION OF WAVES:

The decrease in wavelength as the wave moves from deeper to shallow region is due to decrease in speed of a wave.
-Since the frequency is constant, the wavelength decreases.(v = ƒλ).
-Boundary at angle to the wave, waves are refracted towards the normal; the speed changes causing refraction.

Refraction on curved surface

Refraction can occur when a wave is made to go over a curved surface.
-This can be demonstrated in ripple tank by putting a convex piece of
-Perspex on the surface and water wave made to move over it.