Question

Given below are two statements:
Assertion (A): The Fraunhofer diffraction is produced by the interference between parallel rays. The Fraunhofer diffraction can be observed using two convex lenses.
Reason (R): The two convex lenses are used to observe Fraunhofer diffraction, one to make light from the source parallel and other to focus the light after diffraction on to the screen.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Fraunhofer diffraction is far-field diffraction and is usually observed using lenses to make and focus parallel rays.

Answer 1

The Correct Option is A

Concept:
Fraunhofer diffraction is far-field diffraction. In this type of diffraction, incident and diffracted rays are treated as parallel.

Step 1: Check Assertion.
Fraunhofer diffraction is produced by interference of secondary wavelets in parallel directions. Also, experimentally, it can be observed using two convex lenses. \[ A \text{ is correct} \]

Step 2: Check Reason.
The first convex lens converts light from the source into a parallel beam. The second convex lens focuses the diffracted light on the screen. \[ R \text{ is correct} \]

Step 3: Check explanation.
The reason directly explains why two convex lenses are used for observing Fraunhofer diffraction. \[ R \text{ correctly explains } A \] \[ \therefore \text{Correct Answer is (A)} \]