An intrinsic property of atomic nuclei that influences their acceleration and detection.Charge is an intrinsic property of atomic nuclei and elementary particles that determines how they interact with electromagnetic fields. It is quantified in units of the elementary charge, e, with protons carrying +e and electrons carrying -e. The charge of a nucleus influences its acceleration in electric fields and its detection in particle detectors, as charged particles leave tracks of ionization or light when passing through matter. Charge is conserved in all physical processes, a fundamental symmetry of nature.
The concept of charge was formalized by Benjamin Franklin in the 18th century, who introduced positive and negative charges. The quantization of charge was demonstrated by Robert Millikan's oil-drop experiment in 1909, and the modern understanding of charge as a gauge symmetry was developed in the 20th century.
Charge generates and responds to electric and magnetic fields. In an electric field, a charged particle experiences a force proportional to its charge, causing acceleration. In a magnetic field, a moving charged particle is deflected perpendicular to both its velocity and the field, which is used in accelerators and spectrometers. Detection relies on the particle's charge interacting with detector material: it ionizes atoms, creating electron-hole pairs or scintillation light that can be measured.
Charge is exploited in virtually all electronic devices, particle accelerators like the LHC, and medical imaging techniques such as PET scans, where charged particles are detected to reconstruct images.
The charge of a proton is exactly equal in magnitude to that of an electron, but they are opposite in sign; this balance is why atoms are electrically neutral, and any tiny difference would have profound consequences for the universe's structure.