3. Light
The natural agent that stimulates sight and makes things
visible.
Also called visible electromagnetic radiation that is capable of
causing a visual sensation and has wavelengths from about 380
to about 780 nanometres
4. Characteristics
Light is a form of energy produced by luminous objects.
Light can travel through vacuum.
Light can penetrate through transparent materials but cannot
pass through opaque objects.
Light travels in a straight line in an optically homogeneous
medium.
Light bounces back when made to fall on polished surfaces
such as mirrors or metal surfaces. This bouncing back of light
is described as reflection.
5. The change in the velocity of light when it travels from one
transparent medium to another is described as refraction.
Light appears to have a dual nature. During propagation, light
exhibits wave characteristics but when it interacts with
matter, it behaves like particles.
6. Basic Principles of light
There are four methods of light control:
• Reflection
• Refraction
• Diffusion
• Absorption
7. Reflection
When a ray of light falls on any surface, a part of the light is
sent back to the same medium. This phenomenon where the
incident light falling on a surface is sent back to the same
medium is known as reflection.
There are two types of reflection of light:
• Regular reflection
• Irregular reflection
8. Regular reflection
Regular reflection takes place when a ray of light is incident on
a polished smooth surface like a mirror. Here the reflected ray
of light moves only in a fixed direction.
It is also called as Specular reflection.
Incident light Reflected light
9. Irregular reflection
Irregular reflection takes place when a beam of light is incident
on a wall or wood, which is not smooth or polished.
Also called as diffused reflection or scattering of light.
10. Law of Reflection
The angle of incidence is equal to the angle of reflection.
The ratio reflected light to incident light is known as
reflection factor.
11. Refraction
When a beam of light is passed through a boundary between
two transparent substances having different densities, its
direction is changed.
The light will change its velocity and ‘bend’.
Speed of light in air is very similar to speed of light in a
vacuum
14. Diffusion
When light is incident on a rough surface, it is reflected or
transmitted in many directions at once, this is called diffusion
or scattering.
To prevent glare from a light source, a diffusing glass screen
can be introduced between the observer and the light source.
Two types of diffusing glass are employed. They are:
• Opal glass
• Frosted glass
15. Opal glass: ordinary glass made up of a material having
refractive index different from that of a glass
• Eg: milk glass
Frosted glass: produced by coating ordinary glass with a
crystalline substance
• Eg:
16. Absorption
The taking up and storing of energy, such as radiation, light, or
sound, without it being reflected or transmitted.
17. The absorption of light occurs when a ray of light strikes a
surface. The energy from the light is transferred to the surface
material.
During absorption, the energy may change from one form into
another.
An absorbing surface prevents reflection or diffusion of light
striking on the surface.
