Ray Optics

Light:Light is the form of energy through which we can see objects in our surroundings or can see each other.Light enables us to watch things all around us.

Optics is the term related to light . Light shows different characters.Light has particle nature and wave nature.The terms which are based on rays of light are under the category of Ray Optics.

Various terms related to optics as defined:

Reflection:When light ray strikes on a polished mirror it reflected back or bounces back in the same medium.It is called Reflection.

Here is the diagram:


In the diagram the incoming ray is the incident ray and bounced back ray is the reflected ray.At the point where incident ray and reflected ray meets the surface of mirror, normal is drawn.Normal is the perpendicular line drawn on the surface of mirror. Angle made by incident ray with normal is called Angle of Incidence(i) and angle made by reflected ray with normal is called Angle of Reflection(r).

Laws of Reflection:

1. Normal,incident ray,reflected ray lie on the same plane.

2.Angle of incidence is equal to angle of reflection.

Refraction:When light passes through one medium to other it bends away from its path or track.It is called Refraction. Given diagram shows the refraction.


The light incident on the medium is called Incident ray and the ray passes through the medium is called Refracted ray.Water,air glass are mediums through which the light passes.Angle made by incident ray with normal is same as above incident angle and angle made by refracted ray with normal is called angle of refraction.

Refractive Index: It is the ratio of speed of light in vacuum or air to the speed of light in medium.It is denoted by (μ).

Refractive Index (μ)= Speed of light in air or vacuum/Speed of light in medium.

Laws of Refraction: 1.Incident ray,refracted ray and normal lies on the same plane .

2. Ratio of sine of angle of incidence to the sine of angle of refraction is equal to the refractive index of medium.

Principle of Reversibility :- It states that when light passes through several refractions and reflections .It retraces its path.Just see below diagram . It will be clear to you.


In this diagram we can see that when light passes through air to water refraction occurs. Under the water medium it strikes to mirror and bounces back .Here reflection occurs and then it refracted from water to air. So it repeats its path.This is the principle of reversibilty.

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