Learning Outcomes:

Candidates should be able to:

(c) define the terms used in refraction, including angle of incidence, angle of refraction and normal
 

(d) recall the relationship sin i / sin r = constant
 

(e) apply the relationship between sin i and sin r to new situations or to solve related problems

(f) define refractive index of a medium in terms of the ratio of speed of light in vacuum and in the medium

Law of refraction

• The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane
• For any two given media, the ratio of sine of the angle of incidence over the sine of the angle of refraction is a constant.

Terms used in refraction:

• Incident ray is the ray of light traveling from the source of light through the first medium (i.e. air) to the point of incidence on the surface of the second medium (i.e. glass).
• Refracted ray is the ray of light traveling from the the point of incidence through the second medium.
• Emergent ray is the ray of light traveling from the light out of the second medium
• Normal is the line at right angle to the boundary of the second medium through the point of incidence.
• The angle of incidence, i, is the angle between the incident ray and the normal
• The angle of refraction, r, is the angle between the refracted ray and the normal
• The angle of emergence, e, is the angle between the emergent ray and the normal

Refraction is a very important phenomenon in Physics. It can be used to explain many things including:

(i) Mirages.
(ii) Why the effects of Earthquakes are only felt in certain parts of the World.
(iii) How goggles help you see under water.
(iv) Times of Sunrise and Sunset.

 Refraction is also the reason that bodies of water like swimming pools or ponds always appear to be shallower than they really are.

Rays of light which reflect from the fish travel in a straight line up to the surface of the tank. At the water-air boundary, the waves speed up and as a result, they refract away from the normal. Diverging rays enter the eye and the brain traces these rays back to where it thinks an image is. The result is a virtual image (where the rays appear to converge) at a shallower depth than is the case in reality.

Equilateral Prism:

When white light from ray-box falls on an equilateral prism, it is possible to create a spectrum of colour which can be captured on a white screen.

This effect arises because white light is not a single colour, rather it is made up of many different colours. Each different colour within the white light is refracted by a different amount. Because the entry and exit faces of the prism are not parallel, the effect of the refraction is exaggerated and we see the spectrum. The colours in order of increasing refraction are:

RED
ORANGE
YELLOW
BLUE
GREEN
INDIGO
VIOLET
 

The name for producing a spectrum in this manner is called dispersion.

You may wish to read more about refraction here. View this java applet to know more about the Transmission of Wave through Dense media -- Reflection and Refraction

A screen capture of this java applet in action:

Alternatively, you may check this java applet out too.

A screen capture of this java applet in action:

Formulae to obtain the Refractive Index of a medium