The light gathering power of a camera lens depends on:

In an experiment to measure the focal length $(f)$ of a convex lens,the least counts of the measuring scales for the position of the object $(u)$ and for the position of the image $(v)$ are $\Delta u$ and $\Delta v$,respectively. The error in the measurement of the focal length of the convex lens will be:

In the case of the displacement method of lenses,the product of magnification in both cases is

In the diagram shown,the lens is moving towards the object with a velocity $V \, m/s$ and the object is also moving towards the lens with the same speed. What is the speed of the image with respect to the earth when the object is at a distance $2f$ from the lens? ($f$ is the focal length.)

$A$ convex lens of focal length $12 \ cm$ is made of glass of refractive index $\mu_g = \frac{3}{2}$. What will be its focal length when immersed in a liquid of refractive index $\mu_l = \frac{5}{4}$? (in $cm$)

The radii of curvature for a thin convex lens are $10 \ cm$ and $15 \ cm$ respectively. The focal length of the lens is $12 \ cm$. The refractive index of the lens material is: