Question

In case of a concave mirror, a ray parallel to the principal axis after reflection will

• A. Pass through the principal focus
• B. Diverge from the principal focus
• C. Reflect back to the object
• D. Pass through the centre of curvature

Hint:

For a concave mirror: Parallel ray \(\to\) Passes through Focus (\(F\)).
For a convex mirror: Parallel ray \(\to\) Appears to diverge from Focus (\(F\)).
This is the basic foundation for drawing ray diagrams.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the behavior of a light ray traveling parallel to the principal axis after it reflects off the surface of a concave (converging) mirror.

Step 2: Key Formula or Approach:
This is one of the fundamental rules used in ray tracing for spherical mirrors.

Step 3: Detailed Explanation:

• A concave spherical mirror has a reflecting surface that curves inward. It acts as a converging system.

• The principal axis is the straight line passing through the pole (\(P\)) and the center of curvature (\(C\)) of the mirror.

• According to the laws of reflection, when a beam of light rays parallel to the principal axis falls on a concave mirror, all the reflected rays converge at a single point on the principal axis.

• This specific point of convergence is defined as the principal focus (\(F\)) of the concave mirror.

• Therefore, any individual ray that is parallel to the principal axis will pass directly through the principal focus after reflection.


Step 4: Final Answer:
The ray will pass through the principal focus.