Section Summary

Planck and Quantum Nature of Light

• A blackbody will radiate energy across all wavelengths of the electromagnetic spectrum.
• Radiation of a blackbody will peak at a particular wavelength, dependent on the temperature of the blackbody.
• Analysis of blackbody radiation led to the field of quantum mechanics, which states that radiated energy can only exist in discrete quantum states.

Einstein and the Photoelectric Effect

• The photoelectric effect is the process in which EM radiation ejects electrons from a material.
• Einstein proposed photons to be quanta of EM radiation having energy E=hf,E=hf, where f is the frequency of the radiation.
• All EM radiation is composed of photons. As Einstein explained, all characteristics of the photoelectric effect are due to the interaction of individual photons with individual electrons.
• The maximum kinetic energy KE_e of ejected electrons (photoelectrons) is given by KEe=hf−BE,KEe=hf−BE, where hf is the photon energy and BE is the binding energy (or work function) of the electron in the particular material.

The Dual Nature of Light

• Compton scattering provided evidence that photon-electron interactions abide by the principles of conservation of momentum and conservation of energy.
• The momentum of individual photons, quantified by p=hλp=hλ, can be used to explain observations of comets and may lead to future space technologies.
• Electromagnetic waves and matter have both wave-like and particle-like properties. This phenomenon is defined as particle-wave duality.