Optics Question 921

Question: Radius of curvature of concave mirror is $ 40cm $ and the size of image is twice as that of object, then the object distance is

[AFMC 1995]

Options:

A) $ 60cm $

B) $ 20cm $

C) $ 40cm $

D) $ 30cm $

Show Answer

Answer:

Correct Answer: D

Solution:

$ f=\frac{R}{2}=20cm, $

$ m=2 $ For real image; $ m=-2, $ .

By using $ m=\frac{f}{f-u} $ , $ -2=\frac{-20}{-20-u}\Rightarrow u=-30cm $

For virtual image; $ m=+2 $ .

So, $ +2=\frac{-20}{-20-u}\Rightarrow u=-10cm $



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