LIGHT
UNIT 6
6.1-6.4
RAY DIAGRAMS

Angles are measured between the wave direction (ray)
and a line at 90 degrees to the boundary
o
The line at right angles (90°) to the boundary is
known as the normal
o
The angle of the wave approaching the boundary is
called the angle of incidence (i)
o
The angle of the wave leaving the boundary is called
the angle of reflection (r)

When drawing a ray diagram an arrow is used to show
the direction the wave is travelling
o
An incident ray has an arrow pointing towards the
boundary
o
A reflected ray has an arrow pointing away from the
boundary

The angles of incidence and reflection are usually
labelled i and r respectively
THE LAW OF REFLECTION

The law of reflection states that these angles are the same:

Angle of incidence (i) = Angle of reflection (r)
REFLECTION IN A PLANE MIRROR

A plane mirror refers to a flat surface.

When light rays fall on a mirror, they form an image.

The formation of an image can be understood by using a ray diagram.
REFRACTION OF LIGHT

Refraction occurs when light passes a boundary between two different transparent
media

At the boundary, the rays of light undergo a change in direction

The direction is taken as the angle from a hypothetical line called the normal

This line is perpendicular to the surface of the boundaries and is usually
represented by a straight dashed or dotted line

When drawing a ray diagram an arrow is used to show the direction the wave is
travelling

An incident ray has an arrow pointing towards the boundary

A refracted ray has an arrow pointing away from the boundary

The angles of incidence and refraction are usually labelled i and r respectively
SHOWING REFRACTION
The change in direction depends on which media the light rays pass between:
From less dense to more dense (e.g air to glass), light bends towards the
normal
From more dense to less dense (e.g. glass to air), light bends away from the
normal
When passing along the normal (perpendicular) the light does not bend at all
DISPERSION OF LIGHT

White light is a mixture of all the colours of the
spectrum

White light may be separated into all its colours by
passing it through a triangular prism

This is done by refraction

Violet light is refracted the most, whilst red light
is refracted the least

This splits up the colours to form a spectrum.

This process is similar to how a rainbow is created
DISPERSION: The splitting of light into
different colours
This is the order the colours appear in a
spectrum
PRIMARY COLOURS

Primary colours are those which cannot be made by mixing other colours of
light.

The primary colours are red, green and blue

Red + green= yellow

Red + blue= magenta

Blue + green= cyan

Red + blue + green= white
Every colour other colours are made from a
mixture of the primary colours.
Changing the brightness of the primary colours
makes colours other than yellow, cyan, magenta
and blue
NON-LUMINOUS OBJECTS

Non-luminous objects are those that don’t emit its own light.

A yellow object only looks yellow because it reflects only yellow light,
however it absorbs all the other 6 colourd

A black object absorbs all the light in white light but does not reflect any

A white object reflects all the colours in white light equally