$A$ convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will

The dotted part of the lens is cut and kept on the $x$-axis as shown in the diagram. If parallel paraxial rays are falling on this system,then the coordinate of the image formed after refraction from both the lenses is $(30, -1)$. If $x = 2.5 \, cm$,then $y = .......... \, cm$. (Assume the lens has no spherical aberration)

The distance between a real object and its real image formed by a converging lens is $56 \,cm$. The focal length $f$ of the lens is ............

$A$ convex lens is used to form an image of an object on a screen. If the upper half of the lens is blackened,so that it becomes opaque,then

Write the equation and definition of lateral magnification for a lens.

The diameter of a plano-convex lens is $6 \, cm$ and its thickness at the centre is $3 \, mm$. If the speed of light in the material of the lens is $2 \times 10^8 \, m/s$,the focal length of the lens is.......$cm$.