Question

A concave lens has a focal length of 20 cm. A real object is 30 cm from the lens. Where is the image? What is the magnification?

Answer 1

12 cm and 0.4

Step-by-step explanation:

f = - 20 cm, u = - 30 cm

Let v be the position of image and m be the magnification.

Use lens equation

1 / f = 1 / v - 1 / u

- 1 / 20 = 1 / v + 1 / 30

1 / v = - 5 / 60

v = - 12 cm

m = v / u = - 12 / (-30) = 0.4