Question

What is the colour of a green leaf, when a white light passing through a yellow filter is applied on it?
A. Black
B. Blue
C. Yellow
D. Green

Answer 1

Hint: When light falls on an object, it absorbs some of the wavelengths of light and reflects others. The wavelengths which are reflected, determine the colour of that object. If no light gets reflected, the object appears black.
A yellow filter allows only yellow light to pass through it.

Complete answer:
White light contains all the wavelength of visible light viz. Violet, indigo, blue, green, yellow, orange and red. The colour of the object we see is determined by the wavelengths of white light it absorbs and the wavelength it reflects. For example, tomatoes are red because all the wavelengths of white light are absorbed by tomatoes except red.

Similarly, when white light falls on a green leaf, it absorbs all the wavelengths except green and reflects the green light. That’s why it appears green.

When a white light is passed through a white filter, all wavelengths except yellow light is not allowed to pass through it. It means, only yellow light passes through the filter and when this yellow light falls on the leaf, it gets absorbed. Since, there are no other wavelengths of light, no light is reflected.
Therefore, the colour of a green leaf appears black when a white light passing through a yellow filter is applied on it.

So, the correct answer is “Option A”.

Note:
When light hits an object, the object absorbs some of the light and reflects the rest of it. Which wavelengths are reflected or absorbed depends on the properties of the object.
Those wavelengths which are reflected, determine the colour of the object.