Question

when an object is placed at a distance of 50 cm from a concave spherical mirror the magnification produced is minus one by two where should the object be placed to get a magnification of minus 1 by 5?

Answer 1

Given When an object is placed at a distance of 50 cm from a concave spherical mirror the magnification produced is minus one by two where should the object be placed to get a magnification of minus 1 by 5?

So we have m = - v / u = - 1 / 2

                         - v = m x u

       Given u = 50 cm, m = - 1/2

                        - v = - 1/2 x 50

                          v = 50 / 2 or v = 25 cm

              1 / f = 1 / u + 1 / v

              1 / f = 1 / 50 + 1 / 25

               f = 50 / 3 =  16.6 cm

Now coming to magnification we have

              m = - v / u = - 1 / 5 given

                      v / u = 1 / 5

                        5 v = u

                       v = u / 5 or 1 / v = 5 / u

                 1 / f = 1 /u + 1 / v

                 3 / 50 = 1 / u + 5 / u

                   3 / 50 = 6 / u

                    3 u = 300

                     u = 300 / 3

                     u = 100 cm

Focal length is positive for a concave mirror. The object should be placed at a distance of 100 cm.

Answer 2

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