Question

an object is placed at a distance of 12 cm from a concave lens of focal length 16 cm find the size of an image

Answer 1

1/v+1/u=1/f mirror formula

U=12 focal length =16

1/v= 1/f- 1/u

=1/16- 1/12

v=- 48

m =- (v/u)

=-(-48/12)=4

Answer 2

Sol:- Given

u= - 12cm

f= - 16cm (since concave lens)

v= ?

we know

1/f = 1/v - 1/u

1/v = - 1/f + 1/u

1/v= - 1/-16 + 1/-12

1/v = -3+4/48

1/v= 1/48

v = 48cm

therefore image distance is 48cm

Now,

m= - v/u

m= - 48/-12

m = 4

m= size of image/ size of object

size of image = 4 × size of object.

therefore image is 4 times of the object.