Question

An object is placed $60cm$ in front of a convex mirror of focal length $30cm$. A plane mirror is now placed facing the object in between the object and the convex mirror such that it covers lower half of the convex mirror. What should be the distance of the plane mirror from the object so that there will be no parallax between the images formed by the two mirrors?

• A. $40cm$
• B. $30cm$
• C. $20cm$
• D. $15cm$

Answer 1

The correct option is A $40cm$


For convex mirror,
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\Rightarrow \frac{1}{q}-\frac{1}{60}=\frac{1}{30}\Rightarrow q=20cm$
Plane mirror forms image at the same distance as the object
Hence, for condition of no parallax,
$x=(60-x)+q$
$\Rightarrow x=60-x+20\Rightarrow x=40cm$