We know that when converging beam of light rays are more converging after passing through a surface, then we say the surface is of it positive focal power. If angle of convergence doesn't change it is of zero focal power. Similarly negative focal power diverges.
The formula of focal power of surface when light rays pass from medium of refractive index n1 to medium n2, the focal power is n2-n1/R, where R is radius of curvature of interface.
Now if we consider an plane interface between two different media. Let converging light rays pass through it from denser to rarer. Then the rays become less converging. That is negative power. But according to the above formula ,we should get power as zero(Since R=infinty for plane interface). Why do I get a different answer? Can anyone make out the mistake I did?
As shown in the above figure, Power is non zero. But the formula suggests that power is zero. Why?