Question

A student plots a graph between inverse of magnification \( \frac{1}{m} \) produced by a convex thin lens and the object distance \( u \) as shown in figure. What was the focal length of the lens used?

• A. \( \frac{b}{c} \)
• B. \( \frac{b}{a} \)
• C. \( \frac{a}{b} \)
• D. \( \frac{c}{b} \)

Hint:

The inverse of magnification graph for a convex lens helps determine the focal length by analyzing the slope and intercept.

Answer 1

The Correct Option is C

Step 1: Understanding the graph.
The plot of \( \frac{1}{m} \) against \( u \) is linear. Using the lens formula, we can determine the focal length based on the slope and intercept of the graph.

Step 2: Conclusion.
The focal length of the lens is \( \frac{a}{b} \), which corresponds to option (3).