Question

Assertion : The focal length of an equiconvex lens of radius of curvature $R$ made of material of refractive index $\mu = 1.5$, is $R$.
Reason : The focal length of the lens will be $R/2$.

• A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
• B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
• C. If the Assertion is correct but Reason is incorrect.
• D. If the Assertion is incorrect and Reason is correct.

Answer 1

Answer: (C)

$\frac{1}{f}=(\mu-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)=(1.5-1)\left(\frac{1}{R}-\frac{1}{-R}\right)$
or $f=R$.