Question

A diffraction pattern is obtained using a beam of red light. What happens if the red light is replaced by blue light?

• A. No change.
• B. Diffraction bands become narrower and crowded together.
• C. Band becomes broader and rather apart.
• D. Bands disappear altogether.

Answer 1

Answer: (B)

Diffraction bands become narrower and crowded together.

We know that the width of the diffraction pattern is given by:

As $Y=\frac{\lambda D}{d}$

Since the wavelength of the blue light is smaller than that of the red light, ${\lambda }_{blue}<{\lambda }_{red}$ and width of diffraction bands being directly proportional to $\lambda$, the diffraction bands become narrower and crowded.