Question

A point on the principal axis of a spherical mirror where rays parallel to the principal axis after reflection meet or appear to meet is known as:

• A. centre of curvature
• B. principal focus
• C. pole
• D. aperture

Hint:

Concave mirror \(\to\) Real focus (rays physically meet).
Convex mirror \(\to\) Virtual focus (rays appear to meet when traced back).
Both points are called the principal focus (\(F\)).

Answer 1

The Correct Option is B

Step 1: Compare the candidate terms.
Centre of curvature is the centre of the sphere the mirror is cut from, pole is the midpoint of the mirror's surface, and aperture is the width of the reflecting part, none of these describe where light rays actually converge.
Step 2: Trace parallel rays reflecting off the mirror.
Rays coming in parallel to the axis bend upon reflection and either genuinely cross at one point, or spread out as if coming from one point behind the mirror.
Step 3: Name that convergence point.
That special point, whether rays truly meet there or only appear to when traced backward, is what optics calls the principal focus.
\[ \boxed{\text{Principal focus}} \]