Question

Soap bubble looks colored due to
A. dispersion
B. reflection
C. interference
D. None of these

Answer 1

Hint: We know that the soap bubble is a thin layer or surface of water sandwiched between two layers of soap molecules. The film of soapy water surrounds a bubble of air. The one end of soap repels with water, and the other end attracts, so the molecules move to the inner and outer surfaces.

Complete step by step answer:
The bubble formed by a thin film of water and soap, and it has an outer and an inner surface. Each surface reflects an amount of light, and the waves of both reflections interact with each other, sometimes adding up and sometimes cancelling each other.

Some wavelengths will interfere destructively and other constructively, depending upon the extra distance travelled by a transmitted and reflected ray. This distance depends upon the angle of incident of light and thickness of the film. White light is made up of different colours, corresponding to specific wavelengths. As the thickness of the film changes, at an extra distance, the ray must be changed. Therefore the interference is constructive when the total extra distance matches a specific wavelength of light, and it is destructive when it is a half wavelength. So if white light shines on a bubble, the film reflects light of a specific colour and this colour changes with the film thickness. That means if a soap film is of uniform thickness, different colours are shown. This phenomenon is called interference.

Therefore, the correct option is (C).

Note:
A bubble can exist because the surface layer of a liquid (usual water) has a specific surface tension, which causes the coating to behave somewhat like an elastic sheet. If the distance is more between the water molecules causes a decrease in surface tension, enabling bubbles to form.