Question

A piece of paper appears black in sunlight. What will be the colour when seen in red light?

Answer 1

Hint: We have to discuss the absorbance and reflectance of light. Absorbance refers to those wavelengths of light which are absorbed by a body and hence not reflected. Reflectance refers to those wavelengths of light which are not absorbed and hence reflected. Our eyes see those colours which are reflected, not absorbed.

Complete answer:
It is given in the question that a body appears black in sunlight. Sunlight is white in colour, and constitutes the seven colours of the spectrum. Every light of the spectrum is thus absorbed, or anyone of the colour from the visible spectrum would be perceived by the human eye. Hence, the body absorbs all kinds of wavelengths of light. This type of body is known as black body.

A paper thus appears black, because it has absorbed all the wavelengths of light.If we change the colour from which it has to be seen again. It will absorb all the wavelengths and hence will appear black for any colour as it absorbs all the wavelengths of light.

Note: It must be noted that black objects absorb all wavelengths of light hence all colours of light. While, white objects reflect all colours of light. There is not any reflection when no colour or no wavelength of the light is absorbed. Hence, when we see through any colour it will absorb and not reflect and will eventually appear black.