Ripple Tank Model

Wavelength λ 2.0 cm

Angle of incidence i 40°

Gap width 6.0 cm

How to write it in the exam

A ripple tank is a shallow tray of water. A vibrating bar (the dipper) makes straight wavefronts. A lamp above the tank makes bright lines on a screen below; each bright line is a crest.
A wavefront is a line joining points on a wave that move in step, such as a crest. The wavelength is the distance between neighbouring wavefronts. Wave speed = frequency × wavelength, v = fλ.
Reflection at a plane barrier: the angle of incidence equals the angle of reflection. The speed, wavelength and frequency do not change, so the reflected wavefronts have the same spacing.
Refraction: the waves travel more slowly in shallow water (over a glass plate). The frequency stays the same, so the wavelength decreases and the wavefronts are closer together.
If the wavefronts meet the shallow region at an angle, the waves change direction. When they slow down they bend towards the normal.
Diffraction: waves spread out when they pass through a gap or go past an edge. The wavelength, frequency and speed do not change; draw the wavefronts after the gap with the same spacing.
A narrower gap gives more spreading. The spreading is very noticeable when the gap is about one wavelength wide or smaller. A gap much wider than the wavelength gives little spreading.
For the same gap, a longer wavelength spreads out more. At an edge, waves with a longer wavelength bend further round the edge.