COMEDK · Physics · 25. Ray Optics

Which of the following is a wrong statement?

A \(D=\frac{1}{f}\), where \(f\) is the focal length and \(D\) is called the refractive power of a lens.
B Power is called a clioptre when \(f\) is in metres.
C Power is called a dioptre and does not depend on the system of unit used to measure \(f\).
D \(D\) is positive for convergent lens and negative for divergent lens.

Verified Solution

Answer & Solution

Correct Answer

(C) Power is called a dioptre and does not depend on the system of unit used to measure \(f\).

Step-by-step Solution

Detailed explanation

The power of a lens is given by the reciprocal of its focal length, \(P=\frac{1}{f}\) When \(f\) is in metre, then power \(P\) is in dioptre. Thus, power depends on the system of unit used to measure \(f\).

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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