Question

A concave mirror has a focal length of 40cm . Determine the object for which an eract and four times the size of the object image is formed?​

Answer 1

If you want the image to be erect and magnified, i.e., erect states behind the mirror ie virtual image which is only possible if the object is placed between pole and focus.

height of image = 4x coz let height of object = x

magnificattion = h2 / h1 = -v/u

ie -v/u = 4 therefore v = -4u

mirror formula

1/v + 1/u = 1/f

1/-4u + 1/u = 1/-40

1/u - 1/4u = -1/40

4u-u/4u2 = -1/40

(canceling 40 by 4 to get 10)

3u/u2 = -1/10

(cancelling u by u)

3/u = -1/10

therefore u =-30cm