Refraction of Light Through a Prism

When light passes through one medium to another it bends. This is called refraction.

But, different colours of light will bend differently when they pass through a refracted. Red colour bends most and violet colour bend least.

Light when passed through a glass prism also refracts. Now let's learn about refraction through a glass prism.

Refraction of Light Through a Prism

Now, to find out how light refracts through a prism we need to do an activity using a glass prism, a protractor, some pins, cardboard and a white sheet.

Take the white sheet and stick it to the cardboard. Take the prism and draw its triangular outline as shown.

Now, ΔABC is the prism, ∠A is the called the angle of prism and BC is the baseline. Draw a lined PE where E is on AB.

Put two pins on the anywhere line PE as shown. Now go put your eye on the other side and try to see these pins.

When you see these two pins as shown, move such that the pin P1 is exactly behind pin P2.

When P1 is exactly behind P2, put another pin P3 in that line such that P2 and P1 are exactly behind P3.

Similarly, place another pin P4 in front of the pin P3 so that P3, P2 and P1 are behind the pin P4. Now P1, P2, P3, and P4 appear to be on the same line.

But when you look from above it looks like this.

Join the line P3P4 and extend until it touches the line AC at F and also join the points EF, So the path of the light is P-P1-P2-E-F-P3-P4.

The angle between the incident ray and the normal to AB is called the angle of incidence ∠i. The angle between the refracted ray and the normal to AB is called the angle of incidence ∠r.

The ray coming out of the prism through the side AC is called "emergent ray". The angle between the normal to AC at point F is called "angle of emergence" ∠e.

The angle between the incident ray and the emergent ray is called the angle of deviation ∠D.

This is about how a light ray bends in a prism. Now let's understand dispersion of light through prism.

When white light is passed through a prism it will divide into other colors.

This can be clearly observed in the dark. The white light as shown is refracted a little at the first surface into different colours.

Then the light refracted for the second time, showing clearly all the different colours with which the white light is made of. The White is Light divided into 7 colours (VBGYOR).

This division of white light is called "dispersion of white light". The set of all 7 colours is called "spectrum of white light".

Revision

When a light ray is passed through a prism it undergoes refraction 2 times as shown

The angle prism, angle of incidence, the angle of refraction, angle of emergence, angle of deviation are as shown.

The end