# 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. - Science

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=−6cm

The image height will be = 6 cm.

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