$A$ double convex thin lens made of glass (refractive index $\mu = 1.5$) has both radii of curvature of magnitude $20 \ cm$. Incident light rays parallel to the axis of the lens will converge at a distance $L$ such that $L = ...... \ cm$.

Write the Gaussian equation for a lens.

$A$ thin plano-convex lens of focal length $73.5 \ cm$ has a circular aperture of diameter $8.4 \ cm$. If the refractive index of the material of the lens is $\frac{5}{3}$, then the thickness of the lens is nearly

On which does the convergence capacity of a lens depend?

$A$ lens having refractive index $1.6$ has a focal length of $12 \ cm$ when it is in air. Find the focal length of the lens when it is placed in water. (Take the refractive index of water as $1.28$) (in $mm$)

In many experimental set-ups,the source and screen are fixed at a distance $D$ and the lens is movable. Show that there are two positions for the lens for which an image is formed on the screen. Find the distance between these points and the ratio of the image sizes for these two points.