Question

an object is placed infront of the concave mirror of focal length f.the magnification of the image becomes twice when the object distance is changed from 20cm to 10cm .Calculate the value of f.​

Answer 1

Answer:

ANSWER

It is given that,

Focal length

f=−20cm

hi=3ho

The image is three times the size of the object. So there are two cases.

Case 1. For real image

m=−uv=−3

v=3u

Using mirror’s formula

f1=v1+u1

−201=3u1+u1

u=3−80cm

Case 2. For virtual image

m=u−v=+3

v=−3u

Again using mirror’s formula

−201=−3u1+u1

u=3−40cm

The possible values of u are 3−80cmand3−40cm.