Question

what is the principal focus of a lens

Answer 1

$\textbf{Principal focus of lens}$


$\textsf{Convex lens - }$

The principal focus of a convex lens is a point on its principal axis to which light rays parallel to the principal axis converge after passing through the lens.

Convex lens has real focus.

The focal length of a lens is the distance between optical centre and principal focus of the lens.



$\textsf{Concave \: lens - }$

The principal focus of a concave lens is a point on its principal axis from which light rays, originally parallel to the axis appear to diverge after passing through the concave lens.

Concave lens has virtual focus.

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$\textbf{THANKS }$

Answer 2

\textbf{Principal focus of lens}Principal focus of lens 


\textsf{Convex lens - }Convex lens -  

The principal focus of a convex lens is a point on its principal axis to which light rays parallel to the principal axis converge after passing through the lens.

Convex lens has real focus. 

The focal length of a lens is the distance between optical centre and principal focus of the lens.



\textsf{Concave \: lens - }Concave  lens -  

The principal focus of a concave lens is a point on its principal axis from which light rays, originally parallel to the axis appear to diverge after passing through the concave lens.

Concave lens has virtual focus. 

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\textbf{THANKS }THANKS