Physics

# Refraction of light

## Refraction of light:

When rays of light enter from one transparent medium to another transparent medium, they deviate slightly from their passage on the separate plane of both mediums, this phenomenon is called refraction of light. The reason for the refraction of light is because the speed of light varies in different mediums. ## Some definitions related to the Refraction of Light:

### 1: Incident ray:

A ray of light moving through the first medium that enters the second medium is called an incident ray.

### 2: Refracted ray:

The incident ray when it enters another medium is called a refracted ray.

### 3: Incidence point:

The point at which the incident ray falls on the isolated plane is called the incident point.

### 4:Normal:

The line perpendicular to the isolated plane at the point of incidence is called the normal.

### 5:Angle of Incidence:

The angle between the incident ray and the normal is called the angle of incidence expressed by ‘i’.

### 6: Angle of Refraction:

The angle between the refracted ray and the normal is called the refraction angle expressed by ‘r’.

### 7: Dense medium:

If the incident ray bends towards the normal after refraction, the second medium is called the dense medium relative to the first medium.

### 8: Rare medium:

If the incident ray moves away from the normal after refraction, the second medium is called the rare medium relative to the first medium.

## Laws of refraction of light:

There are two laws of refraction of light –

### First rule:

The incident ray, the refracted ray, and the normal at the point of incidence lie in the same plane.

### The second rule:

For any two mediums, the ratio of the sine of the incidence angle and the sine of the angle of refraction is a constant. This rule is also called Snell’s law and this constant is called the refractive index of the secondary medium relative to the first medium.

sin i/ sin r = n(constant)

n= Refractive index is of the second medium relative to the first medium. Therefore, for any two mediums, the refractive index of the second medium relative to the first medium is equal to the ratio of the speed of light in those mediums. It expresses from ‘n’ the sign of the first and second medium is written on either side of it.

## Types of Refractive Index:

There are two types of refractive index that are explained below.

#### 1:Relative refractive index:

If the first medium is not vacuumed or air then the refractive index of the second medium relative to it is called the relative refractive index.

#### 2:Absolute refractive index:

If the first medium is vacuum or air, then the refractive index of the second medium relative to it is called the absolute refractive index.

Air has the lowest refractive index and diamond has the highest refractive index.

When the refractive index of the two mediums is the same, the incident ray goes straight without deviating, that is, no refraction occurs.

### Relation of refractive index to the speed of light:

The refractive index of a medium is equal to the ratio of the speed of light in a vacuum or air and the speed of light in that medium, and the ratio of the refractive index relative to the air of two mediums is equal to the inverse of the ratio of the speed of light in those two mediums.                                                                                  Refractive Index of Medium (n) = Speed of Light in Vacuum or air (c)/Speed of Light in Medium(v) or

or,      n=c/v

Refractive Index and Speed of Light The refractive index of another medium with respect to an additional medium depends on the color of the light. Its value is highest for purple color and lowest for red color.

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