In the displacement method,we use a lens of focal length $f$ and the distance between the object and the screen is $60 \, cm$. $A$ possible value for the focal length is ........ $cm$.

Write the lens maker's equation for a thin lens.

$A$ biconvex lens has a focal length $2/3$ times the radius of curvature of either surface. The refractive index of the material is:

If the image of an object is at the focal point $f$ to the right side of a convex lens, the position of the object on the left of the lens is at

Is power negative or positive for a concave lens?

$A$ turnip sits before a thin converging lens,outside the focal point of the lens. The lens is filled with a transparent gel so that it is flexible; by squeezing its ends toward its center [as indicated in figure $(a)$],you can change the curvature of its front and rear sides. When you squeeze the lens,the image: