Displacement currents—class room demonstration

摘要

Maxwell’s equations describe the basic laws of electromagnetism. Ampere’s law was not in accordance with the equation of continuity. Maxwell modified this law by introducing displacement current density. This forms the foundation for generation of electromagnetic waves leading to wireless communication. According to this modified Ampere’s law, varying the electric field induces a changing magnetic field. This can be observed in the case of oscillation of charges in a capacitor connected to an alternating voltage source. The concept of displacement current density continues to puzzle the students. A classroom experiment to demonstrate/measure the displacement current density is proposed. Use of a coil–magnet system to generate varying voltage instead of an oscillator makes the setup simpler and cheaper. Also, this method serves multiple objectives of providing clear understanding on the generation of alternating voltage and its visualisation, the behaviour of capacitors, and the extension of this experiment to the working of antennas.