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The image of the flame of a candle, in a...

The image of the flame of a candle, in a concave mirror, is formed at a distance of 30 cm in front of the mirror. Height of the flame is 10 cm and its image is 5 cm high. Distance of the focus from mirror is

A

10 cm

B

15 cm

C

20 cm

D

30 cm

Text Solution

Verified by Experts

The correct Answer is:
C
u = -30 cm
Height of object = 10 cm
Height of image = - 5 cm
`m = (v)/(u ) = (I)/(O )`
`m = (+ 30)/(u ) = (- 5)/(10 )`
u = - 60 cm
Then `(1)/(f) = (1)/(v ) + (1)/(u) `
`(1)/(f ) = - (1)/(30 ) - (1)/(60 ) = (-2-1)/(60 ) `
`f = - 20 ` cm
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