Question

A convex lens of focal length 6 cm is held 4 cm from a newspaper which has print 0.5 cm high. By calculation, determine the size and nature of the image produced.

Answer 1

Given:
Focal length, f = 6 cm
Object distance, u =-4 cm
Size of the object, h = 0.5 cm
Applying lens formula, we get:
1/v-1/u = 1/f
or, 1/v = 1/f + 1/u
= 1/6 + 1/(-4) =-1/12
or, image distance, v =-12 cm
Applying magnification formula, we get:
m = v/u = h'/h

or, m = (-12)/(-4) = h'/0.5

or,  3 = h'/0.5
or,    `h=3xx0.5` 
Size of the image, h' = 1.5 cm
Therefore, the height of the image is 1.5 cm. The value of magnification is positive; therefore, the image is virtual, erect and three times magnified.