Question

A short linear object of length b lies along the axis of concave mirror of focal length f at a short distance u from the pole of the mirror, yhe size of the image is?

Answer 1

Answer:

ANSWER

From mirror formula,

v

1

+

u

1

=

f

1

⟶(1)

Differentiating, we get

⇒−υ

−2

dv−u

−2

du=0

or ∣dυ∣=

∣

∣

∣

∣

∣

∣

u

2

υ

2

∣

∣

∣

∣

∣

∣

du ⟶(2)

Here ∣dv∣=size of image,

∣du∣=size of object (=b)

From the equation 1, we write

v

u

+1=

f

u

Squaring both sides, we get

v

2

υ

2

=(

u−f

f

)

2

Substituting in equation 2 we get

Size of the image dv=b(

u−f

f

)

2