# JEE Main & Advanced Physics Ray Optics Focal Length, Power and Aperture of Lens

Focal Length, Power and Aperture of Lens

Category : JEE Main & Advanced

(1) Focal length (f) : Distance of second principle focus from optical centre is called focal length

${{f}_{\text{convex}}}\to$positive,  ${{f}_{\text{concave}}}\to$negative, ${{f}_{\text{plane}}}\to \infty$

(2) Aperture : Effective diameter of light transmitting area is called aperture. $\text{Intensity of image }\propto {{\text{(Aperture)}}^{\text{2}}}$

(3) Power of lens (P) : Means the ability of a lens to deviate the path of the rays passing through it. If the lens converges the rays parallel to the principal axis its power is positive and if it diverges the rays it is negative.

Power of lens$P=\frac{1}{f(m)}=\frac{100}{f(cm)}$;  Unit of power is Diopter (D)

${{P}_{\text{convex}}}\to \text{positive,}$${{P}_{\text{concave}}}\to \text{negative,}$${{P}_{\text{plane}}}\to \text{zero}$.

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