Question

A magnifying glass is to be used at a fixed object distance of 1 inch if it is to produce an erect image 5 items magnified its focal length should be

Answer 1

Convert the object distance into cm.

1 inch =2.54cm

Magnification) u/v where u is the image distance and v the object distance.

m = 5

5 = u/2.54

u = 2.54 × 5 =12.7cm

The lens formula :

1/f = 1/u + 1/v where F is the focal length.

1/f = 1/2.54 + 1/12.7

100/254 + 100/1270

LCM is 1270

(500 + 100) / 1270 = 600/1270

Getting the reciprocal :

1270/600 = 2.117cm

f = 2.117cm