Assertion : A concave mirror and convex lens | vedclass

Name: Exam Paper Generator | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

(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

Vedclass · Accepted Answer

If both the Assertion and Reason are incorrect.

Vedclass · Answer

(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.

Similar Questions

In the figure shown,a point object $O$ is placed in air on the principal axis. The radius of curvature of the spherical surface is $60\, cm$. Let $I_f$ be the final image formed after all the refractions and reflections. Which of the following statements is correct?

Correct exposure for a photographic print is $10 \, s$ at a distance of $1 \, m$ from a point source of $20 \, cd$. For an equal fogging of the print placed at a distance of $2 \, m$ from a $16 \, cd$ source,the necessary time for exposure is.......$s$.

If $\hat{n}_1$ is the unit vector along the incident ray,$\hat{n}_2$ is the unit vector along the normal,and $\hat{n}_3$ is the unit vector along the reflected ray,then which of the following must be true?

If the luminous efficiency of a lamp is $2 \text{ lumen/watt}$ and its luminous intensity is $42 \text{ candela}$,then the power of the lamp is.......$W$

Vedclass Test Series

Exam Paper Generator

Online Exam Module

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.