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

White light passes through a red filter before arriving at a plane mirror. Then the reflected light passes through a blue filter.
State which colour of light can be seen at each of the points A to D described in the table. Choose the best description of the colour from the list.
[white, red, orange, yellow, green, blue, black (no light passes) ]

Point	Colour of light
A: before the red filter
B: after the red filter but before the mirror
C: after reflection but before the blue filter
D: after blue filter

Accepted Answer

Point Colour of light

A: before the red filter white

B: after the red filter but before the mirror red

C: after reflection but before the blue filter red

D: after blue filter black (no light passes)

A colour filter will only let the light of its own colour pass through it. The absorption of all other colours of light happens in the filter. White light is a mixture of seven different coloured lights which are Red, Orange, Yellow, Green Blue, Indigo and Violet. Here it is given that white light passes through a red filter. Hence, at position A, which is before the red filter, the colour of the light will be white. B is the position that is after the red filter but before the mirror. We know a red filter will only allow red light to pass through it. Hence, at position B, the colour of the light will be red. C is the position after reflection but before the blue filter. We can see that only red colour light is hitting the plane mirror. Hence, the colour of light that is reflected from the mirror will also be red. Hence, at position C, the colour of light will be red. This red light is passing through a blue filter. We know that a blue filter will only allow blue light to pass through it. Hence, the blue filter does not allow the passage of red light through it. Hence, at position D which is after the blue filter, the colour of light will be black.

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