Under the New Cartesian sign convention, which of the following statements is true for a concave mirror?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The focal length of a concave mirror is always negative
In the New Cartesian sign convention, distances are measured from the pole, and those measured in the direction of the incident light are positive while those against it are negative. The object is placed on the left, so light travels to the right. The principal focus of a concave mirror lies in front of the mirror, on the same side as the object, that is against the incident light, so its focal length is always negative. For a convex mirror the focus is behind the mirror and the focal length is positive.