Question

A 3 cm tall object is placed 18 cm in front of a concave mirror of focal length 12 cm. At what distance from the mirror should a screen be placed to see a sharp image of the object on the screen. Also calculate the height of the image formed.

Answer 1

Using mirror equation
`1/v+1/u=1/f`

`⇒1/v+1/(−18)=1/(−12)`

`⇒1/v=−1/12+1/18`

`⇒1/v=(−3+2)/36=−1/36`

`v=−36` cm

Magnification:
`m=−v/u=h_i/h_o`

`m=−((−36)/(−18))`

`m=−2`

`−2=h_i/3`

`⇒h_i=−6`cm

The image height will be = 6 cm.
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