Refraction at spherical surface (n2/v − n1/u = (n2−n1)/R)

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n2/v − n1/u = (n2−n1)/R

What each symbol means

SymbolWhat it stands for
RRadius of curvature of spherical surface (signed)
uObject distance measured along axis from curved surface (signed)
vImage distance from curved surface (signed)
n_1Refractive index where object lies (side of incidence)
n_2Refractive index of second medium (refracted side)

When to use this

Standard JEE / NCERT assumptions unless stated (paraxial, thin lens, coherent YDSE sources, etc.).