Question

Assertion :Focal length of an equiconvex lens of $\mu =3/2$ is equal to radius of curvature of each surface. Reason: It follows from $\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

We Know,

$\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$

For a equiconvex lens of radius of curvature R,

$R_1=R,R_2=-R$

$\frac{1}{f}=(1.5-1)(\frac{1}{R}-\frac{-1}{R})$

$\frac{1}{f}=\frac{1}{2}\times \frac{2}{R}=\frac{1}{R}$

$f=R$

Hence , it comes f=R by the formula,

So , the assertion is true as well as reason is the

Correct explanation of the assertion.

Henceforth Option $\text{A}$ is the correct answer.