Question

F1 and F2 of symmetric convex lens

Answer 1

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here's ur ans

Answer 2

A convex lens or converging lens are the lenses that thicker at the middle. Rays of light are brought closer together when they pass through the lens and the distance between the principal focus and the centre of the lens is called the focal length.

A convex lens consists of two circular arc. when the two arcs of a lens have equal radius, it is called a symmetric lens.

Consider the power of a lens is = D and its focal length is $f_{1}$ and $f_{2}$

The focal length is

$\frac{1}{f}=(n-1)(\frac{1}{R_{1}}-\frac{1}{R_{2}})$ where $R_{1}=-R_{2}$

Where $R_{1}$ and $R_{2}$ are the radius of lens and n is the index of refraction.

As the lens is symmetric. Light travel through the lens from left to right or right to left dose not make an impact on focal length.  

So in this case the lens has two focal points- one on each side. Therefore the $f_{1}=f_{2}$