1.

A 10 mm long awl pin in placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

Answer»

`-30` cm
`-20` cm
`-40` cm
`-60` cm

Solution :As h = 10 m, h. = 5 mm and v = -30 cm, hence `U = (v xx h)/(h.) = ((-30) xx 10)/(5) = -60` cm
So, `(1)/(F) = (1)/(v) + (1)/(u) = (1)/((-30)) + (1)/((-60)) = - (1)/(20) RARR f = -20` cm


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