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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.
Solution
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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