Radius of concave mirror is $40 c m$ and the size of image (real) is twice as that of object, then the object distance is:

60 c m

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20 c m

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40 c m

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30 c m

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Solution

The correct option is D $30 c m$
$F o c a l l e n g t h, f = - 20 c m M a g n i f i c a t i o n, m = - 2 \Rightarrow \frac{- v}{u} = - 2 v = 2 u N o w, \frac{1}{v} + \frac{1}{u} = \frac{1}{f} \frac{1}{2 u} + \frac{1}{u} = \frac{1}{- 20} \frac{3}{24} = \frac{- 1}{20} ∴ u = - 30 c m$

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Radius of concave mirror is 40 cm and the size of image (real) is twice as that of object, then the object distance is:

The correct option is D 30cm Focal length,f=−20cmMagnification,m=−2⇒−vu=−2v=2uNow,1v+1u=1f12u+1u=1−20324=−120∴u=−30cm

Radius of concave mirror is $40 c m$ and the size of image (real) is twice as that of object, then the object distance is:

The correct option is D $30 c m$
$F o c a l l e n g t h, f = - 20 c m M a g n i f i c a t i o n, m = - 2 \Rightarrow \frac{- v}{u} = - 2 v = 2 u N o w, \frac{1}{v} + \frac{1}{u} = \frac{1}{f} \frac{1}{2 u} + \frac{1}{u} = \frac{1}{- 20} \frac{3}{24} = \frac{- 1}{20} ∴ u = - 30 c m$