Name: Colours and Light
Uploaded: 2019-07-19
Duration: 5 min 28 s
Description: Light is made up of wavelengths of light, and each wavelength is a particular colour. The colour we see is a result of which wavelengths are reflected back t...

Question

What do you mean by pure and impure spectrum. Explain with the help of a neat diagram how a pure spectrum can be produced on a screen.

Accepted Answer

A spectrum in which there is overlapping of different colours is called an impure Spectrum. In other words, in an impure spectrum, the colours are not distinct and independent but they overlap. On the other hand, a spectrum with each colour distinct and independent is called a pure spectrum.

A narrow slit S is placed at the focus of a convex lens L1 and is illuminated by white light .The light coming from the slit is made incident on the lens L1. The lens sends out a parallel beam of white rays on to the prism P which is placed in the position of minimum deviation for the yellow.ray . The incident white ray will be dispersed by the prism. Different rays of any one colour will have same angles of incidence and deviation. Hence, the rays will come out as parallel bundle. On account of the difference in the angle of deviation, the angle of emergence will be different for different colours. A second L2 now, focusses different parallel bundles.to different points on the screen M. M is placed at the focal plane of L2 .Thus, all parallel red rays are brought to focus r at one end and all parallel violet rays at v at the other end. A pure spectrum will, therefore, be formed on the screen.

What do you mean by pure and impure spectrum. Explain with the help of a neat diagram how a pure spectrum can be produced on a screen.

Important Questions on Dispersion and Scattering of Light

Learn and Prepare for any exam you want !