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 Q , and so the invariance of the charge corresponds to the vanishing commutator [ Q , H ] = 0 , where H is the Hamiltonian. Thus, charges are associated with conserved quantum numbers ; these are the eigenvalues of the generator 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.