Sign Convention for Refraction by spherical lens
Similar to that of spherical mirror, only the difference is that all the measurement are made from optical centre ‘O’
Few Tips to Remember Sign Convention for Spherical Lens
Lens : f – u – v
Concave : –ve –ve –ve (Real)
+ve (virtual)
Convex : +ve, –ve +ve,
h – is always +ve
n´ – –ve for Real and
+ve for virtual & Errect.
Power of Lens
The degree of convergence or divergence of light ray achieved by a lens is known as power of a lens.
It is defined as the reciprocal of its focal length Represented by P.
SI unit of power of a lens is “dioptre” denoted by ‘D’
I dioptre or ID → It is the power of lens whose focal length is 1m
Power convex lens or converging lens is always positive
Power of concave lens or diverging lens is always negative
If any optical instrument have many lens, then net power will be
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