Optical Center (O)
It is the Center Point of Lens
It is denoted by letter O
Principal Axis
It is the line passing through Center of Lens
It is perpendicular to both faces of lens
Principal Focus (F) of Convex Lens
The point at which
rays parallel to principal axis
coming from infinity converge
after being refracted from Convex Lens
is called the principal focus of Convex Lens
Principal Focus (F) of Concave Lens
The point at which
rays parallel to principal axis
coming from infinity appear to converge
after being refracted from Concave Lens
is called the principal focus of Concave Lens
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Note : - Here we assume ray of light falls from left to right
It is also possible that ray of light falls from right to left
In this case, these lines will converge on other side of lens
This point will be called F'
Hence there are 2 focus (F and F')
(More than 1 focus is called foci)
Focal Length
It is distance between Optical Center (O) and Focus (F)
It is represented by the letter f (small letter f)
