Question

Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose.

(i) State the nature of the lens and the reason for its use.

(ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object?

(iii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use the lens formula to find the position and size of the image.

Answer 1

1. The lens used by the palmist is a convex lens so as to form a magnified image of an object.
2. The palmist should hold the lens at focus, or between the focus and the center of curvature of the lens so as to get the real and magnified image.

$$\begin{gathered} \frac{1}{v}-\frac{1}{u}=\frac{1}{f} \\ \frac{1}{v}=\frac{1}{5}+\frac{1}{10} \\ \frac{1}{v}=\frac{2+1}{10} \\ \frac{1}{v}=\frac{3}{10} \\ v=3.3cm \end{gathered}$$