Question

The magnification of a concave mirror is -1 when an object is placed at 20cm. Find the focal length of the mirror.​

Answer 1

Answer:

10 cm

Step-by-step explanation:

magnification is the directly proportional to negative of image distance from mirror and inversely proportional to distance of object from mirror

i.e: m = -v/u  (v= distance of image from mirror, u= distance of object from mirror )

therefore -1 = -v/-20

                 v = -20

                 we know 1/f=(1/v)+(1/u)

                      therefore; 1/f = (-1/20)+(-1/20)

                                        1/f = -2/20 => f = -10

                                         therefore f = 10 cm.