Exploring Magnetic Resonance with a Compass

Magnetic resonance is a quantum phenomenon and describes a resonant interaction of spins with electromagnetic fields. Its understanding requires advanced knowledge of quantum mechanics and condensed matter physics and thus often remains elusive to students. However, the great impact of this phenomenon on medicine, science, and technology makes magnetic resonance an important subject for general education, and it requires a graspable model for translating the physical concepts without resorting to advanced physics. One of the most common and familiar objects related to magnetism is the compass. Here, we develop an inexpensive tabletop demonstration experiment for magnetic resonance. The compass is placed into the magnetic field of a permanent magnet (strong refrigerator magnet); an alternating field of an electromagnetic coil (solenoid) excites a resonant oscillation of the compass needle. The experiment has been proven to catch the attention of audiences of all ages.