Question

A converging lens has a focal length of 12.5 cm. Construct accurate ray diagrams for object distances of (i) 37.5 cm and (ii) 6.25 cm.

(a) From your ray diagrams, determine the location of each image.

What is the magnification of the images?

Answer 1

Given,

f = 12.5 cm ;

Ray diagrams uploaded (scaling has been done in order for clarity and accomodation in paper)

(i)o = 37.5 cm

We know from lens eqn

1/f = 1/i + 1/o

i = o x f/(o - f)

i = 37.5 x 12.5/(37.5 - 12.5) = 18.75 cm

Hence, i = 18.75 cm

(ii)o = 6.25 cm

i = 6.25 x 12.5/(6.25 - 12.5) = -12.5 cm

Hence, i = -12.5 cm

We know that

M1 = -i/o = -18.75/37.5 = 0.5

M2 = -(-12.5)/6.25 = 2