Lens maker's formula (1/f = (μ−1)(1/R1 − 1/R2))

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1/f = (μ−1)(1/R1 − 1/R2)

What each symbol means

SymbolWhat it stands for
fFocal length of thin lens (m)
R_1Radius of curvature of first surface (signed, Cartesian)
R_2Radius of curvature of second surface (signed)
\muRefractive index of lens material relative to surrounding medium

When to use this

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