Terms Associated with Lenses

Topic Content:

Terms Associated with Lenses:

i. Pole (P): This is the centre of the lens’s curved surface.

ii. Optical Centre (C): This is the centre of the lens.

iii. Principal Axis: is an imaginary line passing through the centre of the lens.

iv. Principal Focus (F) of a lens: is the point on the principal axis where parallel rays close to the principal axis appear to diverge or converge after passing through the lens.

v. Focal Length (f): This is the distance between the principal focus and the optical centre of the lens.

vi. Power of a Lens: this is the reciprocal of the focal length of a lens. P =  \(\frac{1}{f}\)

It is measured in Dioptre (D).

Points on the Principal Axis of Convex and Concave Lens:

The principal axis is the line passing through the optical centre C of the lens.

For a concave lens, F₁ and F₂ are on the opposite side compared to a convex lens. A point that is twice the distance from the