On Fig. 4.3, draw four wave fronts to show what happens to the wave fronts in the shallow water. State how the speed of the waves changes when they enter the shallower water.

When the wave fronts hit the barrier, they reflect. The reflected wave fronts will be parallel to each other, and their direction of travel will obey the law of reflection: the angle of incidence equals the angle of reflection.

A normal line should be drawn perpendicular to the barrier at the point of incidence. The angle between an incident wave front (or ray) and the normal is the angle of incidence, and the angle between a reflected wave front (or ray) and the normal is the angle of reflection. These two angles are equal.

When water waves enter shallower water, their speed decreases, and consequently, their wavelength decreases (since frequency remains constant).

On Fig. 4.3, the incident wave fronts are parallel and perpendicular to the direction of travel. When they enter the rectangular glass block (shallow water), the wave fronts should be drawn closer together than the incident wave fronts, indicating a shorter wavelength. Since the incident wave fronts are parallel to the boundary of the shallow water, the waves will not change direction; they will continue to travel horizontally, but with reduced spacing between them.

When waves enter shallower water, their speed decreases.