Physics - Wave Optics Question with Solution | TestHub
Which of the following condition is TRUE for Fresnel diffraction?
(i) Source of light and the obstacle (slit) are at large distance (infinite) from each other.
(ii) Wavefront incident on the obstacle (slit) is plane.
(iii) The wavefront incident on the obstacle (slit) is either cylindrical or spherical depending on source.
(iv) A convex lens is not required to observe diffraction pattern on the screen.
Options:
Answer:
Solution:
In Fresnel diffraction, the source of light and the screen are at finite distances from the obstacle. Thus, the incident wavefront is either spherical or cylindrical depending on the shape of the source.
Since the distances are finite, no convex lens is required to focus the light rays on the screen.
In contrast, Fraunhofer diffraction involves infinite distances, plane wavefronts, and requires lenses.
Therefore, statements (iii) and (iv) are true.
Answer: (iii) and (iv) are true
