07012022 Refraction of Light Refractive Index Summary Notes

07/01/2022 Refraction of Light Refractive Index (Summary Notes pages 25 -27) Particles and Waves M Ashton 2013

What are we learning today? �That the ratio sinθ 1 /sinθ 2 is a constant when light passes from medium 1 to medium 2. �The absolute refractive index, n, where medium 1 is a vacuum (or air). �The method of measuring the absolute refractive index of glass for monochromatic light. �How to carry out calculations using the relationship for refractive index.

Review of Refraction (simulation)

Activity Refraction L 1: Refractive index and Snell’s law Place the block on the white paper and trace around its outline. Draw in the normal at the midpoint B. With incident angle θ 1 = 10°, measure the angle θ 2, the refracted angle in the perspex. Repeat for the other values of incident angle up to 60 o. . Plot a graph of sin θ 1 against sin θ 2. Simulation

The graph gives a straight line through the origin. �This shows that: �This constant is known as the refractive index, n.

In fact, the absolute refractive index of a material is defined as:

�Refractive index measures the effect a medium has on light. �The greater the refractive index, the greater the change in speed and direction. �The refractive index is always a value greater than, or equal to, 1. �The refractive index of a vacuum is 1. �The refractive index of air is 1. 000277. We use 1 as an approximation.

Absolute Refractive Indices Material Refractive Index, n glass 1. 5 perspex 1. 47 water 1. 33 diamond 2. 4

� comes about because we take the refractive index of air to be 1. �It should really be written as �This is known as Snell’s Law.

Example �Use the information in the diagram to calculate the refractive index of paraffin wax. 340 air n = 1 paraffin wax n = ? n = 1. 43 230

Example �Use the information in the diagram to calculate angle X. 200 air n = 1 perspex n = 1. 47 X = 13 o X

Structured Problems page 37 Qs 87 -93.