Question

The colour of a green leaf, when white light passing through a yellow filter is applied to it is:
(A) Black
(B) Yellow
(C) Red
(D) Green

Answer 1

Hint: Before going into the colour of the leaf, we should know how we see colours in general, for all objects. Objects appear to be of different colours when we observe them because they absorb some colours (wavelengths) and reflect or transmit other colours. The colours we see are the wavelengths that are reflected or transmitted.

Complete step by step answer:
Plants and their leaves look green because the chlorophyll molecules use the red end of the visible white light to power reactions inside each cell. The unused green light is reflected from the leaf and when this reflected light reaches our eyes, we perceive the leaves to be green.
Now, if the white light is passed through a yellow filter, only the yellow wavelength of light will pass through the filter. All the wavelengths of light except that of green light are absorbed by the leaves, and the reflected green light gives the leaf its colour. The yellow filter does not allow the wavelength of green light to pass through. Thus, no colour will be reflected by the leaf making it appear black.
Hence the correct option is (A).

Note: Now, although most leaves are green, there are several colours of leaves found in nature. Leaves get their colours from pigments present in them. While chlorophyll is responsible for the green colour, carotenoid is responsible for yellow, orange and brown colours and anthocyanin is responsible for the red colour. These pigments are responsible for the absorption and the reflection of different wavelengths of light, thus giving the leaves their various colours.
In place of the yellow filter, even if any other filter (except green) is applied to white light, the leaf will appear black.