Question 247: Ray Optics

Question

An object is placed on the principal axis of convex lens of focal length 10cm as shown. A plane mirror is placed on the other side of lens at a distance of 20 cm. The image produced by the plane mirror is 5cm inside the mirror. The distance of the object from the lens is ___________ cm.

Accepted Answer

From diagram
$I_{1}$ is image formed by lens and $I_{2}$ is image formed by mirror.
Location of $I_{1}$ and $I_{2}$ from mirror will be equal $=5 \mathrm{~cm}$ Hence $\mathrm{I}_{1}=15 \mathrm{~cm}$ from lens
From $\frac{1}{v}-\frac{1}{u}=\frac{1}{10}$
$$
u=-x, v=15
$$
$\frac{1}{x}=\frac{1}{10}-\frac{1}{15} \Rightarrow x=30 \mathrm{~cm}$

Ray Optics

An object is placed on the principal axis of convex lens of focal length 10cm as shown. A plane mirror is placed on the other side of lens at a distance of 20 cm. The image produced by the plane mirror is 5cm inside the mirror. The distance of the object from the lens is ___________ cm.

Integer / Numeric Answer Type