Question

The graph below shows the variation of image distance (v) with the object distance (u) when an object is kept in front of a lens. Identify the type of lens used.

Hint:

Remember the key difference from graphs: A convex lens can form real images (\(v>0\)), while a concave lens always forms virtual images (\(v<0\)) for real objects. A positive v on the graph immediately points to a convex lens.

Answer 1

Step 1: Understanding the Concept:
A lens formula relates object distance (\( u \)), image distance (\( v \)), and focal length (\( f \)):
\[ \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \]
Step 2: Detailed Explanation:
The provided graph is a rectangular hyperbola located in a region where \( u \) is negative and \( v \) is positive (indicating real images formed on the opposite side).
For a convex lens, as an object moves from infinity toward the focus, the real image moves from the focus toward infinity. This characteristic curve (where \( v \) decreases as \( |u| \) increases) is unique to a convex lens forming real images.
Step 3: Final Answer:
The lens used is a Convex (converging) lens.