Assertion (A) : Concave mirror is used as doctor's head mirror.

Reason (R) : If a parallel beam of light is incident on a concave mirror, the mirror focuses the beam to a point.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : A student is given a spherical mirror of focal length -10 cm. He identifies it as a concave mirror.

Reason (R) : Focal length of a concave mirror is always positive.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Define centre of curvature of a spherical mirror.

Define radius of curvature of a spherical mirror.