Question
The distance between a convex lens and a plane mirror is $10 \,cm$. The parallel rays incident on the convex lens after reflection from the mirror form image at the optical centre of the lens. Focal length of lens will be.....$cm$
✓
Answer
(b) From the figure,
Using property of plane mirror
Image distance $=$ Object distance
$f -10 = 10 \Rightarrow f = 20{\rm{ }}cm$
Using property of plane mirror
Image distance $=$ Object distance
$f -10 = 10 \Rightarrow f = 20{\rm{ }}cm$
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