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Q.3. A beam of light converges towards a point O, 10 cm behind a concave mirror of focal length 20 cm. Where is the image formed?

(Ans: $v=-\frac{20}{3}cm$)

F = -20 cm

u = -10 cm

Now from the mirror equation we can write that ,

$1/f=1/u+1/v\phantom{\rule{0ex}{0ex}}\Rightarrow -1/20=-1/10+1/v\phantom{\rule{0ex}{0ex}}\Rightarrow 1/v=1/20\phantom{\rule{0ex}{0ex}}\Rightarrow v=20cm$

Regards

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