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Reflection

Reflection is the change in direction of a ray of light at the boundary between two materials. The reflected ray of light stays in the same material it was in before reflection.

Most objects (for example trees) are visible because they reflect light. Very few objects are themselves a source of light.

The sun, a light bulb and a fire are light sources.

You can see your hand because the skin of your hand reflects light.

The sun is reflected in the water, which is reflected in the paddle.
The sun is reflected in the water, which is reflected in the paddle.

Other waves can be reflected, too. An echo is the reflection of sound waves.

The incident ray is the ray of light hitting any surface. If the light is reflected, the resulting ray is called the reflected ray.

A ray of light coming from the sun and hitting the ocean is an incident ray. When we see an image of the sun in the ocean, our eyes sense a reflected ray.

The normal is an imaginary line which is at right angles to the boundary between two materials (e.g. between air and glass).

The angle of incidence is the angle between the normal and the incident ray. It is not measured between the surface and the incident ray.

The angle of reflection is measured between the normal and the reflected ray.

Light reflecting off a boundary. i is the angle of incidence and r is the angle of reflection.
Light reflecting off a boundary. i is the angle of incidence and r is the angle of reflection.

The law of reflection states that the angle of incidence is equal to the angle of reflection.

Light will leave a mirror at the same angle at which it struck it.

The ray of light follows the laws of reflection. $$i$$ is the angle of incidence and $$r$$ is the angle of reflection.
The ray of light follows the laws of reflection. $$i$$ is the angle of incidence and $$r$$ is the angle of reflection.

When you see your eyes in the mirror, the angle of incidence is approximately zero degrees. You can see yourself because the angle of reflection is also zero degrees so the reflected light hits you straight back.