Question

A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms a real image. The new image :

• A. Is closer to the ens system
• B. Is farther from the lens system
• C. Is at the origins position
• D. May be anywhere depending on the focal length of the concave lens

Answer 1

The correct option is D May be anywhere depending on the focal length of the concave lens

When concave lens is put in contact with convex lens, seal/ image is formed i.e. equivalent lens is convex. The focal length of equivalent lens F is greater than focal length of convex lens.
$\frac{1}{V}-\frac{1}{-U}=\frac{1}{f}$
$\Rightarrow \frac{1}{V}=\frac{1}{f}-\frac{1}{U}=\frac{U-f}{fU}$
$V=\frac{Uf}{U-f}=\frac{U}{\frac{U}{f}-1}$
As f increases, $\frac{U}{f}$ decreases $(\frac{U}{f}-1)$ also decreases
Thus, V increases.