Question

a 10 cm long stick is kept in front of a concave mirror having focal length of 10cm in such a way that the end of the stick closest to the pole is at a distace of 20 cm. what will be the length of the image ?

Answer 1

m=hi/ho. or -v/u
=-20/-20=1
m=1
m=hi/ho
1=hi/10
hi=10 cm ans

Answer 2

Question :-

A 10 cm long stick is kept in front of a concave mirror having focal length of 10 cm in such a way that the end of the stick closest to the pole is at a distance of 20 cm. What will be the length of the image ?

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Answer :-

Given :

Image distance ( v ) = 20 cm

Object distance ( u ) = ?

focal length ( f ) = 10 cm

By Len's formula :

1 / f = 1 / v - 1 / u

In convex lens :

u is negative always.

v is negative

f is negative

==> 1 / ( - 10 ) = 1 / - v - 1 / ( - 20 )

==> - 1 / 10 = - 1 / v + 1 / 20

==> - 1 / v = 1 / 10 - 1 / 20

==> 1 / v = - ( 2 - 1 ) / 20

==> 1 / v =  -1 / 20

So v = - 20

Given :

Image height ( I ) = ?

Object height ( O ) = 10 cm

By Linear magnification :

v / u = I / O

==> v / u = I / 10 cm

==> ( -20 ) / ( -10 ) = I / 10

==> 2 / 1 = I / 10

==> I = 2 × 10

==> I = 20 cm

The length of the image will be 20 cm !

Hope your doubt is cleared :)

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