Reflection by Circular Barriers

reflection of light off a mirror

When a set of plane (straight) waves reflect off a semi-circular barrier, they are focused to a point (see left).

The red lines show the direction in which the plane waves are travelling.

Like all reflections, the incidence angle equals the angle of reflection.

The semi-circular barrier focuses the waves to exactly half the distance from the centre of curvature.

The final set of curved blue lines shows the waves after reflection. These will pass through the point of focus and back out the other side.