Refraction and Angle of Incidence

Introduction

• Refraction is the change in direction of a ray of light as it passes from one optical material into another.
• The behaviour of light at the boundary between two materials depends on the angle at which it strikes the surface.

Normal Incidence

• When a ray of light is incident at normal incidence, meaning it strikes the surface at right angles (perpendicular), it travels in a straight line through the material without changing direction.
• In this case, there is no bending of the light ray.

Non-Normal Incidence

• When the ray of light strikes the surface at any other angle, it changes direction as it enters the new material. This bending of the light ray is called refraction.
• The angle between the incoming ray and the imaginary line perpendicular to the surface is measured and is known as the angle of incidence.

Calculation of Refractive Index

• The change in direction of a ray of light during refraction depends on the change in the speed of light as it passes from one material to another.
• The refractive index (n) of a material can be calculated using the formula:
• n = c / v
• Where:
  • n is the refractive index of the material.
  • c is the speed of light in a vacuum (or air, as an approximation).
  • v is the speed of light in the material.
• When using this formula, the angle (θ) must always be the angle of incidence in a vacuum (or air).

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Refraction and Angle of Incidence

Dependence on Frequency and Colour

• The refractive index depends on the frequency or colour of light.
• Light with a higher frequency (shorter wavelength) has a greater refractive index than light with a lower frequency (longer wavelength).
• This phenomenon explains why a prism can disperse white light into its various colours, creating a spectrum.

Small Change in Refraction

• It's important to note that the change in refraction is generally small and only significant for specific geometries and conditions.

Summary

• Refraction is the change in direction of a light ray as it enters a different material.
• Normal incidence results in no bending of the light ray, while non-normal incidence leads to refraction.
• The refractive index of a material can be calculated using the formula n = c / v.
• The refractive index varies with the frequency or colour of light, with higher-frequency light having a greater refractive index.
• The change in refraction is typically small and significant only in certain situations.