Refraction of Light
Refraction of Light
Basic Principles
- Light waves change speed when they pass from one medium to another; this change in speed causes them to bend, a process known as refraction.
- The amount by which light bends, or refracts, depends on the refractive index of the two materials, the angle of incidence, and the wavelength of the light.
- As a rule, light slows down and bends towards the normal - an imaginary line perpendicular to the surface at the point of incidence - when moving to a denser medium.
- Conversely, light speeds up and bends away from the normal when moving to a less dense medium.
- The principle of refraction is also the basis for lenses and how they form images.
Laws of Refraction
- The law of refraction, also known as Snell’s Law, states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given frequency.
- In formulaic terms, this is n= sin i / sin r, where n is the refractive index, i is the angle of incidence, and r is the refractive index.
Types of Refraction
- When light enters a medium with a higher refractive index (denser medium), it bends towards the normal. This is called negative or normal refraction.
- When light enters a medium with a lower refractive index (rarer medium), it bends away from the normal. This is called positive or inverse refraction.
Effects and Uses of Refraction
- Refraction in a prism can disperse white light into its component colours, forming a spectrum. This occurs because different colours of light refract by different amounts.
- Lenses use the principle of refraction to focus light waves. Examples include magnifying glasses, cameras, glasses, and contact lenses.
- The lens in the human eye works by refracting light to create a sharp image on the retina.
- Optical fibres operate based on the principle of total internal reflection, a form of refraction.
Refraction Experiments
- Experiments with prisms, lenses, ray boxes, and pools of water can demonstrate refraction.
- To measure refractive indices of glass and water, you will need to use a semicircular glass block and a ray box.
- By changing the angle of incidence and observing the angle of refraction, you can determine the refractive index of the material.