Light

LIGHT

• ​Reflection

• Refraction

• Dispersion

• Colours of light

Reflection

​Ray diagrams of relection

• Light travels in straight line.
  The path of light is called ray.

• A ray coming onto a surface, such a mirror, is called incident ray.

• The line perpendicular to mirror is called normal.

• The angle between the incident ray and the normal is called angle of incidence (i).

Reflection

• A ray coming away from the mirror is called reflected ray

• The angle between the reflected ray and normal is called angle of reflection (r).

• The low of reflection: the angle of reflection is equal to the angle of incidence (i = r).

Reflection

​Reflection on concave mirror

Refraction

​Broken pencil in water

• The pencil appears to be broken at the surface of the water because of refraction.

• Refraction of light is the change in direction of light on passing from one medium to another because of change in speed.

• Medium is material that light passes through.

​Medium	​Speed of light in km/s
​air	​300 000
water​	225 000​
glass​	200 000​

Refraction

• The light passing from air into glass or water is bent towards the normal.

• It means the refracted ray is closer to the normal than it would be if the incident ray just carried on in a straight line

• The angle of incidence is greater than the angle of refraction

Refraction

• The light passing from water or glass into air is bent away from the normal.

• It means the refracted ray is further away the normal than it would be if the incident ray just carried on in a straight line.

• The angle of refraction is greater than the angle of incidence.

Dispersion

• Dispersion mean splitting light into different colours.

• Dispersion happens because light is refracted.

• Each of different colours of light that make up white light can be refracted through a slightly different angle using a triangle prism.

Dispersion

• The range of colours that can be seen in white light is called spectrum.

• There are seven colours in the order that they appear in the spectrum, they are: red, orange, yellow, green, blue, indigo, and violet (ROY G BIV).

Colour of Light

• There are three colours of light from which all other colours of light can be made. These are called primary colour.

• The primary colours are: Red, Green, and Blue.

• The primary colours cannot be made by mixing any other colours of light.

• The colours in light mix differently from the colours in paint.

Colour of Light

• You can remove colours from light using coloured filter.

• If transparent piece of coloured glass or plastic is place in front of a wight light, then only light of that colour will be transmitted (get through). All of other colours will be abseorbed.

​Traffic lights use coloured filters

Colour of Light

• When you look at a non-luminous object, you see the light that is reflected from the object. Non-luminous means the object does not emit its own light.

• A white object reflects all the colours in white light equally.

• A black object absorbs all colours in white light and does not reflect any.

• Red objects only reflect red light and absorb all other colours.

• Blue objects only reflect blue light and absorb all other colours.

​Red object