Question

23. Your friend is unable to distinguish convex and concave lenses. What questions
do you ask him to understand about convex and concave lenses?
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Answer 1

Answer:

A convex lens is thicker at the centre and thinner at the edges. A concave lens is thicker at the edges and thinner at the centre. Due to the converging rays, it is called a converging lens. Due to the diverging rays, it is called a diverging lens.

Convex and concave lens can be distinguished by touching them. If the curved surface is bulging outwards then it's convex lens and if the curved surface is curved inwards then it's concave lens.