Physics Light

You can have a view of yourself if you look into

a mirror.

calm water surface.

a piece of shiny metal wall.

a piece of window glass.

Now you look into a mirror and see the image of yourself.

In front of the mirror.

On the surface of the mirror.

Behind the mirror.

A ray of light bounces off a plane mirror.

mirror

This is an example of reflection of light.

reflected rayincident ray

normal

mirror

angle of incidence

angle of reflection

• The incident ray, the reflected ray and the normal all lie in the same plane.

normal

incident ray reflected ray

mirror

normal

incident ray reflected ray

mirror

normal

incident ray reflected ray

mirror

• angle of incidence angle of reflection =

Regular reflection

parallel incident rays

parallel reflected rays

• on a flat, smooth surface• e.g. mirror

Regular and diffuse reflection

Diffuse reflection

• on a rough, not perfectly smooth surface

• e.g. cover of a book

parallel incident rays

reflected rays in different directions

Regular and diffuse reflection

Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The

phenomenon is mainly in governance to the law of conservation of energy. The proper explanation

would be that due to change of medium, the phase velocity of the wave is changed but

its frequency remains constant. This is most commonly observed when a wave passes from one medium to another at any angle other than

90° or 0°. Refraction of light is the most commonly observed phenomenon, but any type of wave can

refract when it interacts with a medium, for example when sound waves pass from one

medium into another or when water waves move into water of a different depth.

The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane.

For any two given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

And the third law is called Snell’s law

Snell's law  is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water and glass.

Snell's law states that the ratio of the sins of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the opposite ratio of the indices of refraction:

with each θ as the angle measured from the normal, v as the velocity of light in the respective medium (SI units are meters per second, or m/s) and n as the refractive index (which is unit less) of the respective medium.