Question

In which colour a yellow coloured dress would appear when viewed through a blue filter?
A. Yellow
B. Blue
C. Black
D. Green

Answer 1

Hint: A coloured filter is an optical instrument which filters out some wavelengths of lights and blocks the other wavelengths. A blue filter would only allow blue colour light to pass through and this is based on the principle of subtractive colour mixing.

Complete step by step answer:
Yellow light is a mixture of combination of red and green lights. When we see the yellow coloured dress directly through our eyes it appears yellow as when white light is incident on the dress it absorbs all the other colours and reflects only yellow light. This dress appears yellow to us as the light receptors in our eyes send signals to the brain and we can see the colour.
The purpose of a filter is to transmit the wavelength of that colour of the filter and block all other wavelengths. So when light is transmitted through a blue filter it blocks the other wavelengths and allows 90% of the wavelength of blue light to pass through.
Now, when the light rays reflected from the yellow dress go through the blue filter it filters out the yellow light which is a mixture of red and green lights. Thus, no colour light coming from yellow dress can pass through the blue filter and the dress would appear black when seen through the blue filter.
The correct answer is option C. Black

Note: Students must remember that the colour of an object is not its inherent property. What we see through our eyes is because of the functioning of our eyes and brain and their way of preserving colours. What we see is light rays reflected from a surface after absorption of all other wavelengths.