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A man uses a concave mirror for shaving. He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal lengt.1 of the mirror |
Answer» Correct Answer - C `u=-25cm` `=m=(A_1B_1)/(AB)=u/v` `rarr 1.4 =-(v)/(-25)` `rarr 14/10=v/25` `rarr v=(25xx14)/10=35 cm `Now, 1/f=1/v+1/u` `rarr 1/f=1/35-1/25 `=(5-7)/175=-2/175` `rarr f=-87.5` so, focal length of the concave mirror is 87.5 cm. |
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