Question

Write Einstein’s photoelectric equation. How did Millikan prove the validity of this equation?

Hint:

Einstein’s photoelectric equation provides a direct relationship between the energy of the incident light, the work function of the material, and the kinetic energy of the emitted electrons. Millikan confirmed the validity by his precise measurements of stopping potential and electron energy.

Answer 1

Step 1: Einstein’s photoelectric equation, \( E_{\text{kin}} = hu - \phi \), describes the energy balance. Here, \( E_{\text{kin}} \) is the photoelectron's kinetic energy, \( h = 6.626 \times 10^{-34} \, \text{J s} \) is Planck's constant, \( u \) is the incident radiation frequency, and \( \phi \) is the material's work function (minimum energy to eject an electron). The incoming photon energy is consumed by the work function, with any surplus becoming the electron's kinetic energy.

Step 2: Millikan's experiment confirmed Einstein's equation by measuring the stopping potential needed to halt photoelectrons. By measuring maximum photoelectron kinetic energy at different light frequencies, he verified the linear kinetic energy-frequency relationship predicted by Einstein's equation.