Question

i. What is principal focus of a spherical refracting surface?
i​

Answer 1

The central point of a lens is known as Optical centre of Lens. The line passing through the optical centre of the lens is known as Principal Axis. ... This point is known as the Principal Focus. Since a lens has two convex surfaces, thus a lens is said to have two foci.

Answer 2

Answer:

The central point of a lens is known as Optical centre of Lens. The line passing through the optical centre of the lens is known as Principal Axis. ... This point is known as the Principal Focus. Since a lens has two convex surfaces, thus a lens is said to have two foci.

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