Question

In order to obtain a magnification of -0.5 with a convex lens of focal length 10 cm, the object should be placed:

Answer 1

Answer: 30 cm away from the lens

Explanation:m = v/u

So, v = mu = -.5u

Now,

1/f = 1/v - 1/u

or 1/f = 1/(-.5u) -1/u

or 1/f = -3/u

or u = -3f

or u = -3*10 (since f = 10 CM)

or u = -30 cm