1.

An object is placed at a distance of 15 cm from a concave mirror and its real image is formed at 30 cm in front of that mirror. The focal length of the mirror is

Answer»

`+ 20` CM
`-20` cm
`-10` cm
`+10` cm

SOLUTION :Here u = - 15 cm and v = - 30 cm, hence
`(1)/(f) = (1)/(v) + (1)/(u) = (1)/((-15)) + (1)/((-30)) = (-2-1)/(30) = - (1)/(10) rArr f = - 10` cm


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