Charge (physics)

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In physics, a charge is any of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges correspond to the time-invariant generators of a symmetry group, and specifically, to the generators that commute with the Hamiltonian. Charges are often denoted by ${\displaystyle Q}$, and so the invariance of the charge corresponds to the vanishing commutator ${\displaystyle [Q,H]=0}$, where ${\displaystyle H}$ is the Hamiltonian. Thus, charges are associated with conserved quantum numbers; these are the eigenvalues of the generator ${\displaystyle Q}$. A "charge" can also refer to a point-shaped object with an electric charge and a position, such as in the method of image charges.