Final answer:
A quantum of light is called a photon, which is a zero mass particle of electromagnetic radiation that carries a quantum of energy. Photon theory emerged as part of wave-particle duality, helping explain phenomena like the photoelectric effect and light intensity as a measure of photon count, not wave amplitude.
Step-by-step explanation:
The quantum of light is called a photon. This term refers to a particle of electromagnetic radiation with zero mass that carries a quantum of energy. The concept of photons emerged from the work of theorists like Albert Einstein who helped to describe the photoelectric effect. In this model, light is seen not just as a wave, but as being composed of particles, or photons, with Einstein proposing that each photon moves at the speed of light and possesses energy, which is quantified by the equation E = hf, where E is the energy of the photon, f is the frequency of the light, and h is Planck's constant.
The idea of photon emerged from the realization that electromagnetic waves are not continuous, smooth waves, but instead, they are absorbed and emitted in lumps or quantized packets of energy. This theory helped explain several phenomena, including why the intensity of light is independent from the amplitude of light waves but instead depends on the number of photons. In everyday encounters with light, such as from a typical light bulb, we do not notice individual photons because they are emitted in such large numbers.