The radius of curvature of a spherical mirror is half of the focal length.

Which of the following statements about light waves is $NOT$ correct?

What is the $SI$ unit of the power of a lens?

The image formed by a lens is always erect and diminished. What is the nature of the lens?

$A$ $5 \, cm$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $20 \, cm$. The distance of the object from the lens is $30 \, cm$. Find the $(i)$ position,$(ii)$ nature,and $(iii)$ size of the image formed.

An object $1 \, cm$ tall is placed at a distance of $15 \, cm$ from a concave mirror of focal length $10 \, cm$. Find the position,size,and nature of the image formed.