A Coulomb null experiment is described that enables physics students to obtain rigorous upper bounds on photon mass. The experimenter searches for subnanovolt signals that would escape a closed shell were photon mass to be positive. The approach can be adapted for several college levels. At the simplest level, a ‘‘miniature’’ low‐cost experiment allows a student to verify the exponent ‘‘−2’’ in Coulomb’s law to eight or more decimal places. An advanced student given a full‐size apparatus (at greater cost) can obtain mass bounds very close to the established laboratory limit.

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