Question

To obtain an image of magnification -0.5 where should one place an object in front of lens of power 10 D

Answer 1

Power = 10D

So f=100/P

= 100/10

= 10cm

m= -0.5

So, the lens is convex lens as image is real, inverted and diminished.

One formula for magnification is

m= f/f+u

f+u = m x f

u = m x f - f

u = -0.5 x 10 - 10

u = -15

But as object distance is always negative

-u= -15

u= -(-15)

u = 15 cm

Therefore the object should be placed 15 cm from the lens on the left hand side.