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  Aim : To study the dispersion of white light by a glass prism.

Appartus Required : A glass prsm, a card board having a narrow rectangular slit, a white screen.

Procedure : 

• Take a thick sheet of cardboard and make a small hole or narrow slit in its middle.

• Allow sunlight to fall on the narrow slit. This gives a narrow beam of white light.

• Now, take a glass prism and allow the light from the slit to fall on one of its faces as shown in figure.

• Turn the prism slowly until the light that comes out of it appears on a nearby screen.

• We will find a  beautiful band of colours.

Observation and Conclusions : The glass prism splits the incident white light into a band of colours. The various colours are seen in the sequence:

Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR). This band of the coloured components of light beam is called its spectrum. The splitting of white light into its component colours is called dispersion.

Different colours of light bend through different angles with respect to the incident ray, as they pass through the prism. The red light bends the least while the violet bends the most. Thus the rays of different colours emerge along different paths and become distinct. Thus we see bands of different colours on the screen in the form of a spectrum.