Assertion : A concave mirror and convex lens | vedclass

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(D) The focal length of a mirror is given by $f = R / 2$,which depends only on the radius of curvature $R$ and is independent of the surrounding mediu

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If both the Assertion and Reason are incorrect.

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(D) The focal length of a mirror is given by $f = R / 2$,which depends only on the radius of curvature $R$ and is independent of the surrounding medium. Thus,the focal length of the concave mirror remains unchanged in water.For a lens,the focal length $f$ is given by the Lens Maker's Formula: $\frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$,where $n$ is the relative refractive index of the lens material with respect to the medium. When the lens is placed in water,the relative refractive index decreases,causing the focal length of the lens to increase.Therefore,the focal lengths of the mirror and the lens will not be the same in water. The Assertion is incorrect.The refractive index of water $(n \approx 1.33)$ is greater than the refractive index of air $(n \approx 1.0)$. Therefore,the Reason is also incorrect.

Assertion : $A$ concave mirror and convex lens both have the same focal length in air. When they are submerged in water,they will have same focal length.
Reason : The refractive index of water is smaller than the refractive index of air.

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Assertion : $A$ concave mirror and convex lens both have the same focal length in air. When they are submerged in water,they will have same focal length.Reason : The refractive index of water is smaller than the refractive index of air.