Photoelectric Effect Calculator

What Is the Photoelectric Effect? The photoelectric effect is the emission of electrons from a material when light shines on it. Albert Einstein explained it in 1905 in Germany, showing that light behaves as particles (photons), each carrying energy proportional to its frequency. This discovery earned him the Nobel Prize in Physics in 1921.

Einstein’s Photoelectric Equation KE_max = hf - W (or equivalently, KE_max = hc/lambda - W). Where KE_max is the maximum kinetic energy of ejected electrons. h is Planck’s constant (6.626 x 10^-34 J*s). f is the frequency of incident light. c is the speed of light (3 x 10^8 m/s). lambda is the wavelength. W (phi) is the work function of the material.

The Work Function The work function is the minimum energy needed to remove an electron from the material’s surface. Each material has a characteristic work function. Cesium has one of the lowest at 2.1 eV, making it very sensitive to light. Platinum has a high work function of 5.65 eV. Most metals fall between 2 and 5 eV.

Threshold Frequency Below a certain frequency (the threshold frequency), no electrons are ejected regardless of light intensity. The threshold frequency f_0 = W/h. This was unexplainable by classical wave theory, which predicted that any light of sufficient intensity should eject electrons.

Key Observations That Confirmed the Photon Theory Increasing light intensity increases the NUMBER of ejected electrons but not their kinetic energy. Increasing light frequency increases the kinetic energy of each electron. Below the threshold frequency, no electrons are ejected at any intensity. Electrons are emitted instantly — no time delay as classical theory would predict.

Common Work Functions (eV) Cesium: 2.1. Potassium: 2.3. Sodium: 2.75. Calcium: 2.87. Zinc: 3.63. Copper: 4.65. Silver: 4.26. Gold: 5.1. Platinum: 5.65. These values mean cesium responds to visible light, while platinum requires ultraviolet light.