Question

a divergent lens has a focal length of 20 cm .at what distance should an object height 4 cm from the optical centre ot the lens be placed so that its image is formed 10 cm away from the lens . find the size of the image also ?

Answer 1

f = - 20 cm

h1 = 4 cm

v= - 10,

u = ?

h2 =?


$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

1 / u = - 1 / 20 + 1 / 20

= -1 / 10 + 1 / 20


= -2 + 1 / 20

= - 1 / 20.

u = -20 cm

h(i) = v / u . h(0)

= -10 cm/ 20 cm × 4

= 2cm

Answer 2

$<b><u><i>$Refer to the both attached files

$<b><u><i>$Using lens formula

$<b><u><i>$u = - 20cm

$<b><u><i>$h2 = 2cm