Electronvolt (eV)
The electronvolt, symbolized as eV, is primarily used in atomic, nuclear, and particle physics. It is the energy gained by an electron moving through a one-volt potential. The electronvolt enables scientists to measure very small energy changes at the atomic scale. Introduced in the early 20th century, it is standard for describing energy in atoms, photons, and particles. The electronvolt adds the necessary precision in modern physics and works in conjunction with larger units, such as joules and kilojoules.
Kilocalorie (kcal)
The kilocalorie, symbolized as kcal, equals 1,000 calories and is often referred to as a “Calorie” with a capital C in food labeling. It measures the energy in food and human metabolism, helping dieticians, nutritionists, and consumers track intake. The kilocalorie became the standard unit of energy measurement as nutrition science linked energy measurement to diet. Most scientists now use joules, but kilocalories are still commonly used in reporting food energy.