Question

a short linear object of lenght b lies along the axis of a concave mirror of focal length f at a distance u from pole of mirror. the size of image is

1) [f / (u-f)] b

2) [f / (u-f)]2 b

Answer 1

Let distance of image from pole be v.

According to mirror equation.

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

Multiply both side by u

u / f = u /v + 1

u -f / f = u/v

Multiply both side by -1

f - u/ f = 1/m

or magnification m = f / f - u

$Size of image \: = m \times size \: of \: image$

Size of image = f / f - u * b

Answer 2

Answer:length of image =magnification^2*length of object

=(f/u-f)^2*b

Length of image=m^2.b

=(v/u)^2.b

=(f/u-f)^2*b