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 $
