An equiconvex lens of radius of curvature $14 \ cm$ is made up of two different materials. The left half and right half of the vertical portion are made up of materials with refractive indices $1.5$ and $1.2$ respectively,as shown in the figure. If a point object is placed at a distance of $40 \ cm$,calculate the image distance. (in $cm$)

An object is placed at $15 \, cm$ from a convex lens of focal length $20 \, cm$. Which of the following is correct?

$A$ 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,you can change the curvature of its front and rear sides. Suppose that the image must be formed on a card which is at a certain distance behind the lens,while you move the turnip away from the lens,then you should

$A$ candle placed $25 \ cm$ from a lens forms an image on a screen placed $75 \ cm$ on the other side of the lens. The focal length and type of the lens should be

The radius of curvature of the convex surface of a thin plano-convex lens is $15 \ cm$ and the refractive index of its material is $1.6$. The power of the lens is

$A$ real object approaches a fixed diverging lens with a constant velocity from infinity along the principal axis. The relative velocity between the object and its image will be