Question

An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm.

(a) Use lens formula to find the distance of image from the lens.

(b) Draw a ray diagram to justify your answer in part

Answer 1

(a) We need to calculate the image distance. 

Given, u = -60 cm, f = -30 cm, v =? 

Using lens formula, 

1/v - 1/u= 1/f 

1/v = 1/f + 1/u 

1/v = -1/30 -1/60 = -1/20 

v = -20 cm 

The diminished image is formed on the same side as the object and at a distance of 20 cm from the lens. 

(b)