Question

what is the difference between concave and convex lens?

Answer 1

Concave:-

It is made by polishing the inner surface of the mirror.

Light after reflection converge.

It form a real and inverted image.
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Convex:-
It is made by polishing the outer surface.

Light diverge after reflection

It form a virtual and erect image.

Answer 2

$\textbf{Concave lens }$:

It is thinner at the edges and thicker in the middle.

It is a converging lens

It mostly forms real images

$\textbf{Concave lens }$:

It is thinner in the middle and thicker at the edges.

It is a diverging lens.

It always forms virtual images.