Ans. REFRACTION OF WAVES
When waves from one medium enter in the second medium at some angle their direction of travel may change. This phenomenon is called refraction of waves.
The speed of a wave in water depends on the depth of water. If a block is submerged in the ripple tank, the depth of water in the tank will be shallower over the block than elsewhere. When water waves enter the region of shallow water, their wavelength decreases .But the frequency of the water waves remains the same in both parts of water, because it is equal to the frequency of the vibrator.
For the observation of refraction of water waves, we repeat this experiment such that the boundary between the deep and the shallower water is at an angle to the wave front. Now we will observe that in addition to the change in wavelength, the waves changes their direction of propagation as well The direction of propagation is always normal to the wave fronts. This change of depth of water waves while passing from a region of deep water to that of shallower is called refraction.