# Aim To determine the refractive index of a material and the speed of light in order to calculate the expected critical angle at which total internal reflection occurs

by ashunboi1 (student)

Practical Experiment 3:

Refraction and Reflection of Light

Aim

To determine the refractive index of a material and the speed of light in order to calculate the expected critical angle at which total internal reflection occurs.

Hypothesis

As the sin of the angle of incidence increase, the sin of the angle of refraction also increases

Theory

There is a strong relationship between the angle of incidence and angle of refraction of lights. Light can pass through different materials, assuming that it is transparent. It can also pass through two different isotropic materials such as air to glass. When light passes from one isotropic material with a high refraction index to another isotropic material with a lower refraction index, there is an angle where light passing through gets reflected and refracted (Young 2011). Snell brought up a law, which determines the angle at which light bends according to the initial angle and also the refraction index of materials. Where he derived the formula;

where

= refractive index of material a

= refractive index of material b

= sin of angle of incidence

= sin of angle of refraction

(Young 2011)

However light may not be refracted all the time, as there is a point where the light will not pass the second material, this is when light gets reflected at the surface. This angle is known as the angle of refraction.

Equipment:

Light Box                                Semi-circular Prism Protractor

Method:

1. Using the light box, shine the light at the semi-circular prism protractor at an of angle 0°
2. Record the angle at which light is refracted
3. Repeat step 1-2 but for 10°, 20°, 30°, 40°, 50°, 60°, 70° and 80°.

Note: see diagram below for details

Results

Relationship Between Angle of Incidence and Angle of Refraction

Table 1.1                Resolution: Protractor = 1°

Graph of the Sin of the Angle of Incidence and Angle of Refraction

Graph 1.1

From Snell’s law, the gradient (1.55) of the graph is =

;

Hence to determine the refractive index of the semi-circular prism protractor, Snell’s law formula must be use

given that

is the refractive index of air, which is 1.000293, and

x

x 1.000293

...