Reflection: The Law of Reflection and Mirror Images

0:00When light hits a mirror, which way does it bounce?

0:04The ray of light coming in is called the incident ray.

0:08Where it hits, we draw the normal, a line at 90 degrees to the mirror.

0:13The angle between the incident ray and the normal is the angle of incidence.

0:19The ray going out is the reflected ray, at the angle of reflection.

0:24The law of reflection: these two angles are always equal.

0:29A smooth surface, like a mirror, reflects parallel rays all one way.

0:35A rough surface, like paper, has bumps facing many ways, so it scatters light every way.

0:42So rough surfaces do reflect light, and every ray still obeys the law.

0:47Now stand a plane mirror, a flat one, upright with an object in front.

0:53Light from the object reflects into your eye. Your brain traces it straight back to an image behind the mirror.

1:00The image is upright, the same size, and as far behind the mirror as the object is in front.

1:07If the object is 1.5 metres in front, its image is 1.5 metres behind.

1:14A concave mirror caves inward. Parallel rays reflect and meet at one point, the focal point.

1:22A flashlight does the reverse: a bulb at the focal point sends out a straight beam.

1:29A convex mirror bulges outward. It spreads rays apart, giving a wide view, like safety mirrors in shops.

1:38Every surface, flat or curved, smooth or rough: the angle of incidence equals the angle of reflection.