Question

A dentist use a mirror in front of a decayed tooth at a distance of 4 cm from the tooth to get a 4 times magnified image. Use mirror formula to find the focal length and nature of mirror used. What is the nature of image?

Answer 1

Hope this helps you buddy ,

ATQ , u = -4

         magnification (m) = +4

m = -v/u    ⇒   4 = -v / -4   ⇒ 4 *-4 = -v

     so , -16 = -v

           v = 16 cm .................................................(i)

HERE IT'S CLEAR THAT IT IS A CONCAVE MIRROR BECAUSE IT ONLY GIVES ERECT MAGNIFIED IMAGE WHEN KEPT   B/W   F AND P

          (Note that here v is (+ve) indicating that image is formed behind the mirror)

now using mirror's formula , we will find the focal length ,

1/f = 1/v + 1/u

1/f = 1/16 + (-1/4)

1/f = 1/16 - 1/4

1/f =  1-4/16

1/f = -3/ 16

f = -16/3

IMAGE IS VIRTUAL , ERECT AND MAGNIFIED , FORMED BEHIND THE MIRROR

MIRROR USED - CONCAVE MIRROR