Question

Choose the incorrect statement out of the following.

• A. If we cut two spherical mirrors from same sphere, they must have same radius of curvature.
• B. The direction of incident ray is chosen to be positive.
• C. A concave mirror with very large aperture is chosen to focus the incident beam of parallel rays at a point.
• D. The focal length of plane mirror is infinity.

Answer 1

The correct option is C A concave mirror with very large aperture is chosen to focus the incident beam of parallel rays at a point.

In order to focus the incident beam concisely to a single point, the region of the incoming incident beam needs to be restricted. This can be achieved by using a concave mirror with very small aperture $\left(AB\right)$ compared to its radius of curvature.

Why this question? Caution: For spherical mirrors of large aperture, focus will not be a single point.