What type of lens behaviour will an air bubble inside water show?

An object of height $5 \, cm$ is placed perpendicular to the principal axis of a concave lens of focal length $10 \, cm$. If the distance of the object from the optical centre of the lens is $20 \, cm$,determine the position,nature,and size of the image formed using the lens formula.

At what distance should an object be placed to obtain its real,inverted and of same size image as the object by a convex lens?

An object is placed $50\, cm$ from a lens that produces a virtual image at a distance of $10\, cm$ in front of the lens. Calculate the focal length of the lens. (in $, cm$)

What is meant by power of a lens? Define its $SI$ unit. You have two lenses $A$ and $B$ of focal lengths $+10\, cm$ and $-10\, cm$ respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed $8\, cm$ from the lens? Draw a ray diagram to justify your answer.

Give the mathematical expression for the power of a lens.