Question

the focal length of the concave mirror is 10. an object is placed in front at the distance of 8cm find the magnifications for the image.

Answer 1

Let magnification be m

So m= height of image/ height of object

So m= 3

Also m= -v/u (v is image distance and u is object distance

So 3 = -v/-10 ( u is negative 10 because it is always negative)

Thus v= 30

Now use the mirror formula i.e

1/f = 1/v + 1/u

And solve this

The answer is -15

Answer 2

f = -10 cm
u= -8 cm

Formula
1/v + 1/u = 1/f

1/v = 1/f - 1/u
= -1/10 - (-1/8)
= -1/10+ 1/8
= -8+10/80
= 2/80
= 1/40
v = 40

Magnification = -v/u
= -40/-8
= 5