Question

The condition for observing Fraunhofer diffraction pattern from an obstacle is that the light wavefront incident on it must be

• A. spherical
• B. plane
• C. cylindrical
• D. either cylindrical or spherical

Hint:

Fraunhofer diffraction always involves plane wavefronts.

Answer 1

The Correct Option is B

Step 1: Types of diffraction.
Fraunhofer diffraction is observed when both the source and the screen are effectively at infinite distances from the obstacle.
Step 2: Nature of wavefront.
Under these conditions, the incident wavefront becomes plane.
Step 3: Eliminating incorrect options.
Spherical and cylindrical wavefronts correspond to Fresnel diffraction, not Fraunhofer diffraction.
Step 4: Conclusion.
The wavefront must be plane.