Question

A four times magnified image of an object formed by a concave mirror of focal length 20cm,can be taken
nna screen. Find the position of the object and screen.​

Answer 1

Answer:

position of object from mirror = 25 cm, position of screen from mirror = 100 cm

Explanation:

Since a real image is formed, so magnification m = -4 ... (1) (real image formed from concave mirror is always inverted)

Also, we know m = - v/u ... (2), and 1/v + 1/u = 1/f ... (3)

using (1) and (2), we get v = 4u .. (4), and it is given that f = -20.

Now, using (4) and (3), we get

1/4u + 1/u = 1/(-20), or u = -25

Now, using (4), we get, v = - 100

The minus sign here shows that, focus, object and screen are in opposite direction of incident ray when measured from pole of the mirror.