Einstein's Photoelectric Equation

Einstein's photoelectric equation from NCERT states that the maximum kinetic energy of an emitted electron equals the photon energy minus the work function, written $K_{max}=h\nu -\varphi$. This expresses energy conservation: a single photon spends part of its energy freeing the electron and the remainder becomes the electron's kinetic energy. Substituting the given values, $K_{max}=5.0-2.3=2.7$ eV. The value 7.3 eV is wrong because it adds the work function instead of subtracting it, violating energy conservation. The value 3.5 eV is wrong because it uses an incorrect work function value not supplied in the problem. The value 2.3 eV is wrong because it simply repeats the work function, which is the energy consumed, not the leftover kinetic energy. As stated in NCERT Class 12, Chapter 11, only the photon energy in excess of the work function appears as electron kinetic energy, and this linear relationship was Einstein's crucial insight. A magnitude check confirms that with a 5.0 eV photon and a 2.3 eV barrier, the surplus 2.7 eV sensibly represents the fastest electrons emitted.