## Quick Reference

*E* = mc ^{2}, where *E* is a quantity of energy, *m* its mass, and *c* is the speed of light. It presents the concept that energy possesses mass.

*E*_{max} = hf – *W*, where *E*_{max} is the maximum kinetic energy of electrons emitted in the photoemissive effect, *h* is the Planck constant, *f* the frequency of the incident radiation, and *W* the work function of the emitter. This is also written *E*_{max} = hf – φ*e*, where *e* is the electronic charge and φ a potential difference, also called the work function. (Sometimes *W* and φ are distinguished as work function energy and work function potential.) The equation can also be applied to photoemission from gases, when it has the form: *E* = hf – *I*, where *I* is the ionization potential of the gas.

*Subjects:*
Chemistry — Physics.