Assertion: The focal length of an equiconvex lens placed in air is equal to radius of curvature of either face. Reason: For an equiconvex lens radius of curvature of both the faces is same.

Question

Assertion: The focal length of an equiconvex lens placed in air is equal to radius of curvature of either face. Reason: For an equiconvex lens radius of curvature of both the faces is same. (A) If both assertion and reason are true and reason is the correct explanation of assertion (B) If both assertion and reason are true but reason is not the correct explanation of assertion (C) If assertion is true but reason is false (D) If both assertion and reason are false

Tardigrade Admin · Accepted Answer

For an equiconvex lens, R1 = R2 = R From (1/f) = (μ -1) ((1/R1)-(1/R2)) [using lens makers formula] For lens, μ = 1.5 placed in air. Therefore, (1/f) = (1 .5 -1 )(2/R) ⇒ f = R,

Q. Assertion : The focal length of an equiconvex lens placed in air is equal to radius of curvature of either face.
Reason: For an equiconvex lens radius of curvature of both the faces is same.

If both assertion and reason are true and reason is the correct explanation of assertion

If both assertion and reason are true but reason is not the correct explanation of assertion

If assertion is true but reason is false

If both assertion and reason are false

For an equiconvex lens, $R_{1} = R_{2} = R$
From $\frac{1}{f} = (μ - 1) (\frac{1}{R _{1}} - \frac{1}{R _{2}})$
[using lens makers formula]
For lens, $μ = 1.5$ placed in air.
Therefore, $\frac{1}{f} = (1.5 - 1) \frac{2}{R}$
$\Rightarrow f = R$ ,

Q. Assertion : The focal length of an equiconvex lens placed in air is equal to radius of curvature of either face. Reason: For an equiconvex lens radius of curvature of both the faces is same.