Question

What is the focal length of a
lens.​

Answer 1

Attachment fig. of Answer

$\huge \text{Answer :-}$

The ${\sf\underline{\orange{focal~lenght}}}$ of a lens is defined as the distance between the principal of focus & optical centre.

$\huge \text{About~It :-}$

A ${\sf\underline{\green{lens}}}$ is a piece of a refrecting medium bounded by two surfaces at least one of which is curved surface.

The commonly used lenses are the spherical lenses. These lenses have either both surfaces spherical or spherical and the other a plane one.

${\sf\underline{\purple{Lenses~can~be~divided~into~two~categories :-}}}$

(i) Convex or converging lenses.

(ii) Concave or diverging lenses.

A Convex Lens :-

It is thicker at the centre than are the edges. It converges a parallel beam of light on reflection through it. It has a real focus.

Types of Convex Lenses :-

(a) Double convex or biconvex lens is the lens, having both surfaces of convex.

(b) Planoconcave lens is the lens, where one side is convex and the other is plane.

(c) Concavoconvex is the lens, In which one side is convex and the other is Concave.

Types of Concave lenses :-

• Double convex is the lens, both sides are concave.

• Planoconcave lens where, one side is plane and the other is concave.

• Convexoconcave lens where, one side is convex and the other is concave.

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Hope it's helpful :)

Answer 2

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