Question

What are the necessary conditions which are to be followed to obtain a pure spectrum on a screen?

Answer 1

Step 1: Definition of the spectrum:

The band of seven colors formed on a white screen, when a beam of white light is passed through a glass prism, is known as a spectrum of white light. The colors which appear in the spectrum of white light are violet, indigo, blue, green, yellow, orange, and red (VIBGYOR).

Step 2: Diagrammatic representation of impure and pure spectrum:

1. Pure Spectrum: A spectrum in which the dispersion is highly discriminative so that at each point the light is practically monochromatic.
2. Impure Spectrum: A spectrum in which there is overlapping of different colors is called an impure spectrum.

Step 3: Conditions of the pure spectrum:

For obtaining a pure spectrum following conditions should be satisfied:-

1. Rays coming out from convex lens should have parallel incidence,
2. Prism should be in the condition of minimum deviation,
3. Emerging light rays should be focused through an achromatic lens.