Question

A spherical mirror and a thin spherical lens have each a focal length of -15çm The mirror and and the lens are likely to be

Answer 1

both are likely to be concave. plz mark as brain list answer.

Answer 2

The focal  length of a spherical mirror = - 15 cm
   Then it is a concave mirror. Because the direction of focus from the pole of the mirror is in the direction opposite to that of the light rays from the object.

Focal length of a spherical lens = - 15 cm
    Then the lens is equivalent to a biconcave lens.  This is because the direction of the principal focus is opposite to the direction of the light rays from the object.

This is due to the sign convention chosen by scientists and physicists.