Question

If in the previous example we use a diverging lens with a focal length 10 cm to form an image of the pencil kept 15 cm in front of the lens, locate and characterise the image.

Answer 1

In accordance with Cartesian sign convention the given parameters are

f = -10 cm, u = -15 cm 

From lens equation, we have 

(1/v) = (1/f) + (1/u) 

= [1/(-10)] +[1/(-15)] = -(1/6) 160 

v = -6 cm 

Lateral magnification, m = (v/u) = -6/-15 = 0.40 

The minus sign with image shows that the image is located on the side of the object. The magnification is positive and m <1, which shows that the image is upright and diminished.