Combined Lens Power – Rankers Physics

Lens Makers Formula/ Len's Formula: Practice Problem & Solution

Assertion (A): When two thin equiconvex lens are placed in contact, the effective power of combination may decrease. Reason (R): Power of lens is defined as ability of bending of light.  
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Lens Makers Formula/ Len's Formula. Understanding the underlying formula is key to arriving at the correct answer below:

For two thin lenses in contact, the equivalent power is \(P = P_1 + P_2\). For equiconvex lenses, both \(P_1\) and \(P_2\) are positive. Therefore, the effective power (P) will always increase, not decrease. Thus, (A) is false.
Power of a lens is indeed a measure of its ability to bend or converge/diverge light rays. Thus, (R) is true.
Therefore, (A) is false but (R) is true.

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