Light is form of energy which enables us to see objects which emit or reflect light.

Light is a type of (form of) energy which can produce sensation in our eyes. So we can experience the sensation of vision.
It is travel in straight line in form of particles and waves. With the help of light we see all colours of nature.

Our eyes are mostly sensitive for yellow colour and least sensitive for violet and red colour. Due to this reason commercial vehicle’s are painted with yellow colour, sodium lamps are used in road lights.

Properties of light

Light energy propagates (travels) via two processes.

  1. The particles of the medium carry energy from one point of the medium to another.
  2. The particles transmit energy to the neighbouring particles and in this way energy propagates in the form of a wave.
  3. It propagates in straight line.
  4. It’s velocity in vacuum is maximum whose value is 3 × 108 m/sec. (297489978 m/s)
  5. Light does not need a material medium to travel that is it can travel through a vacuum.
  6. It exhibits the phenomena of reflection refraction, interference, diffraction, polarization and double refraction.

Ray of light

A straight line which show the direction moment of light is called ray of light.

beam of light

A bunch of light rays or bundle of rays at a point is called beam of light.

ray-of-light & beam of light

How we see?

When a light ray is falling (strike) on the surface of any object which reflect and reached to our eyes. Due to this our eyes feel a sensation then we see the object.

Reflection of light

When rays of light falls on any object it return back in the same medium from the surface this phenomenon is called reflection of light. Due to reflection of light we can see all the nature.

Incident ray

The ray of light which falls on a polished surface (or a mirror) is called the incident ray of light.

Reflected ray

The ray of light which gets reflected from a polished surface (or a mirror) is called the reflected ray of light


The normal is a line at right angle to the reflecting surface.


Laws of reflection

  1. The incident ray, the reflected ray and the normal to the surface at the point of incidence all lie in the same plane.
  2. The angle of incidence (∠i) is always equal to the angle of reflection (∠r) i.e. ∠i = ∠r


Laws of reflection
  • When a ray of light falls on a mirror normally or at right angle it gets reflected back along the same path.
Laws of reflection

Depending on the nature of the reflecting surface, there are two types of reflection :-

(i) Regular (specular) reflection

(ii) Irregular (diffused) reflection

Regular reflection

When parallel light rays fall on smooth plane surface like mirror, if all rays of light are reflected parallely along a difinite direction. Then this kind of reflection is called regular reflection.