Question

Wave front due to light source situated at infinity is:

• A. Spherical.
• B. Cylindrical.
• C. Plane.
• D. None of the above.

Hint:

A light source at infinity creates plane wavefronts because the rays are parallel when they reach the object.

Answer 1

The Correct Option is C

Step 1: Understanding the concept.
When a light source is located at infinity, the light rays reach the object in parallel, and the wavefronts formed are plane waves. This is because the distance is so large that the curvature of the wavefront is negligible.
Step 2: Analyzing the options.
(1) Spherical: This is incorrect. Spherical wavefronts occur when the light source is a point source.
(2) Cylindrical: This is incorrect. Cylindrical wavefronts occur when the source is along a line.
(3) Plane: Correct. A light source at infinity produces parallel rays, resulting in plane wavefronts.
(4) None of the above: This is incorrect, as option (3) is correct.
Step 3: Conclusion.
The correct answer is (3) Plane, as the wavefront formed by a light source situated at infinity is a plane wave.