Einstein photo-electric equation states that \( E_k = h\nu - \varnothing \). In the equation, \( E_k \) refers to
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Maximum kinetic energy of the emitted electrons
In Einstein’s photoelectric equation the whole photon energy \( h\nu \) goes to the electron; part of it, the work function, is spent in leaving the metal, and the rest appears as kinetic energy. This is the largest possible kinetic energy, for an electron that comes from the surface level of the metal.
Electrons that are more tightly bound lose some extra energy on the way out, so they emerge with less than \( E_k \). Hence \( E_k \) is neither the energy of all the electrons, nor their mean, nor their minimum value; it is the maximum kinetic energy.
NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… If this quantum of energy absorbed exceeds the minimum energy needed for the electron to escape from the metal surface (work function φ0), the electron is emitted with maximum kinetic energy
\( \displaystyle K_{max} = h\nu - \phi_0 \qquad (11.2) \)
More tightly bound electrons will emerge with kinetic energies less than the maximum value.”