Question

Power of a biconvex lens is \( P \) diopter. When it is cut into two symmetrical halves by a plane containing the principal axis, the ratio of the power of two halves is:

• A. 1:2
• B. 2:1
• C. 1:4
• D. 1:1

Hint:

When a lens is cut along the principal axis, its focal length remains unchanged, and hence its power remains the same.

Answer 1

The Correct Option is D

Step 1: {Understanding the Concept of Lens Power} 
The power of a lens is given by: \[ P = \frac{1}{f} \] where \( f \) is the focal length of the lens. 
Step 2: {Effect of Cutting a Lens Along the Principal Axis} 
When a symmetrical biconvex lens is cut into two halves along the principal axis, the focal length remains the same for each half.
Since power is inversely proportional to focal length, the power of each half remains unchanged.
Thus, the ratio of power between the two halves is: \[ 1:1 \] Thus, the correct answer is \( 1:1 \).