The law of reflection tells us that angle of incidence and angle of reflection are equal:
The reflection of a ray of light works in just the same way as a ball bouncing off a wall,
except gravity has no noticeable effect on light rays.
Refraction
In addition to reflecting light, many surfaces also refract light: rather than bouncing off
the surface, some of the incident ray travels through the surface, but at a new angle. We
are able to see through glass and water because much of the light striking these
substances is refracted and passes right through them.
Light passing from one substance into another will almost always reflect partially, so
there is still an incident ray and a reflected ray, and they both have the same angle to the
normal. However, there is also a third ray, the refracted ray, which lies in the same
plane as the incident and reflected rays. The angle of the refracted ray will not be the
same as the angle of the incident and reflected rays. As a result, objects that we see in a
different medium—a straw in a glass of water, for instance—appear distorted because the
light bends when it passes from one medium to another.