An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power -10D. Find the size of the image.

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Solution

Given:
u = - 15 cm , v = ?
$h_{o}$ = 4 cm , $h_{i}$ =?
P = -10D
f =1/P= - 1/10 m = -10cm
Using lens formula
1/v - 1/u = 1/f
1/v + 1/15 = - 1/10
1/v = - 1/10 - 1/15
= - 5/30
= - 1/6
v = - 6 cm
Using magnification formula:
$m = \frac{h_{i}}{h_{o}} = \frac{v}{u}$
$h_{i}$ = (- 6/- 15) * 4
= 24/15
= 1.6 cm

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An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power -10D. Find the size of the image.

Given:u = - 15 cm , v = ?ho = 4 cm , hi =? P = -10D f =1/P= - 1/10 m = -10cmUsing lens formula 1/v - 1/u = 1/f 1/v + 1/15 = - 1/10 1/v = - 1/10 - 1/15 = - 5/30 = - 1/6 v = - 6 cmUsing magnification formula: m=hiho=vu hi = (- 6/- 15) * 4 = 24/15 = 1.6 cm