In what year was the magnetic effect of an electric current first measured, and by whom?

The magnetic effect of an electric current was first measured in 1820 by Hans Christian Ørsted, which is closely associated with Andre Ampere's further developments in electromagnetism. Ørsted discovered that an electric current produces a magnetic field, which was a groundbreaking realization that laid the foundation for the field of electromagnetism.

Though the question options do not mention Ørsted directly, Andre Ampere, who contributed significantly to the understanding of the relationship between electricity and magnetism around this time, is notably recognized for his work establishing the principles of electromagnetism. In 1820, the connection between electric currents and magnetic fields was first documented through experiments, establishing this significant milestone in physics.

The other figures mentioned in the options contributed to electrical theory but did not measure the magnetic effect of electric current in the same significant way during that particular year. For instance, Faraday's major contributions came later, and Ohm is primarily recognized for Ohm's Law in 1826, which describes the relationship between voltage and current, not the magnetic aspects of electricity. Heinrich Hertz' experiments in the late 1800s were pivotal for electromagnetic waves, but irrelevant to the initial measurement of the magnetic effect of an electric current.