Refraction

When sound waves and light waves travel from one medium to another and there’s a change in density, for example from air to glass, they change direction at the boundary of the mediums. This is called refraction.

For example, when a ray of light hits a block of glass at an angle both its speed and its direction changes. When it leaves the block it bends back to its original direction.

• The angle of incidence (i) is the angle from the normal at which the light (incident ray) entered the block of glass.
• The angle of refraction (r) is the angle at which the incident ray refracted away from the normal.

When the ray of light travels into the block it bends towards the normal. The angle of refraction inside the block is less than the angle of incidence.

However, if the waves cross the boundary at 90