Question

Yuri investigates light and coloured filters. He shines white light through a red filter and then a green filter.

What is the colour of the light at A and B?

Answer 1

We need to analyse the coloured filters given in the question and find out what wavelengths of colours they filter out and what is the resultant light coming out of it. We need to know about the concept of colour subtraction: when light falls on any filter, some components of light are absorbed by the filter whereas some are transmitted.

Complete answer:
A filter is a transparent medium that allows only a specific light to pass through it and all the other components of the incident light get absorbed by the filter when white light shines on it.Therefore in the given experiment done by Yuri, when the white light shines through a red filter, the filter only allows red light to pass through it and the other components of the white light get absorbed.

And hence the colour of light at A will be rad colour light.Similarly, when the red light will pass through the green filter, the green filter will only allow the green colour to pass through it and will absorb the rest of the components. And hence the red light incident on it will be absorbed and no light will pass through the filter and it will appear black at B.

Note: Note that when white light is incident on different coloured filters, the whole spectrum of the white light consisting of seven colours is not dyed with the colour of the filter instead the other colours or the wavelengths of the spectrum is absorbed and the light of the colour of the filter remains. This is called colour by subtraction.