Question

A white source of light during interference forms only white and black fringes. Width of fringe is inversely proportional to the wavelength of the light used.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

If both assertion and reason are false

Answer 2

Fringe width $\beta=\frac{\lambda D}{d}.$ This depends on the wavelength. Diffraction depends on the wavelength of light. Therefore if a white source of light is used, only the central fringe will be white. All the rest have different wavelengths and some orders will also overlap for different colours.