Question

The minimum distance between an object and its real image formed by a thin convex lens of focal length f is Kf. Find the value of K.

• A. 1
• B. 4
• C. 3
• D. 2

Answer 1

The correct option is B

4

Since object and image is real,

Object distance = $-x_1$
Image distance = $x_2$

$x_0=x_1+x_2;\frac{1}{x_2}-\frac{1}{-x_1}=\frac{1}{f}$

$\Rightarrow x_1+x_2=\frac{x_1{x}_2}{f}$

Solving above equations for real values of $\frac{x_1}{x_2}$

We get

$x_0=4f,\therefore K=4$