Question

How could you show that the colours of the spectrum combine to give white light?

Answer 1

Hint: White light, when it passes through the prism it splits into a spectrum of seven colour rays which is called spectrum of white light, here we will design a setup experiment to show that this spectrum of colours combine to form again white light.

Complete Step By Step Answer:
• When white light passes through the prism it splits into seven colours namely- Violet Indigo Blue Green Yellow Orange Red in increasing order of their wavelengths. and This phenomenon is known as dispersion of light.
• Now, let us place a prism, namely first prism and another prism inverted with respect to the second prism namely prism B and behind the prism B a black screen is placed as shown in the diagram.
• In the below diagram, the orange colour spectrum represents the combined seven colours spectrum of white light.

• When a white light passes through first prism it gets dispersed in to seven colour spectrum represented by orange band and this spectrum of white light when passes through another inverted second prism the emergent ray again became white light and this phenomenon is called recombination and on black screen we can observe the white spot of light easily.
• Hence, this is the desired setup experiment to show that the colours of the spectrum combine to give white light.

Note:
It should be remembered that, for ease of diagram the orange band is simply draw to represent the spectrum otherwise in reality this spectrum will consist of all those seven colours in order of increasing wavelength sometimes most commonly referred as VIBGYOR where each letter represent first letter of these seven colours of white light spectrum.