Question

The figure shows Fraunhoffer's diffraction due to a single slit. If first minimum is obtained in the direction shown, then the path difference between rays $1$ and $3$ is

• A. $0$
• B. $\lambda / 4$
• C. $\lambda / 2$
• D. $\lambda$

Answer 1

Answer: (C)

In Fraunhoffer diffraction, for minimum intensity, $\Delta x=m \frac{\lambda}{2}$
For first minimum, $m =1 \therefore \Delta x =\frac{\lambda}{2}$