Physics (NTSE/Olympiad)  

5. Human Eye & Colourful World

Dispersion Of White Light By A Glass Prism

Dispersion Of White Light By A Glass Prism
When a ray of white light (sunlight) enters a glass prism (denser medium). It emerges out and broken into seven colours.
This phenomenon, due to which different components of a white light are separated is called (dispersion)
Explanation : It is due to different refractive index of different components of white light.
White light has seven colours, namely, violet indigo, blue, green, yellow, orange and red (remembered by the word VIBGYOR ). In air (strictly in vacuum) light waves of all colours have same velocity (3 × 108 m/s).
But in a denser medium, their velocities become less and different. Red light waves, being longest in length, travel fastest and have maximum velocity. Violet light waves, being shortest in length, travel slowest and have minimum velocity in the denser medium.
The refractive index (µ)of a medium for a wave is given by the relation.

As µ is maximum for violet so it bends maximum

When this dispersed white light is made to fall on a white screen, we get a seven coloured band or light. This coloured band is called spectrum.

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