Prior to engaging in studies of electromagnetic devices, an examination of simple yet very important devices made of permanent magnets is due. In the diagram below, a magnet is used to control a switch that regulates the flow of electricity in a circuit:
In order to close the circuit and elicit flow of electric current ( I ) from the cathode ( – ) to the anode ( + ) of the source, the magnet is moved within close vicinity of the switch:
The utility of such devicess is derived from their low cost and ability to be placed within environments that are to rugged or hazardous for human operators. In this case, physical motion places the magnet where it needs to be to close the switch. A de-energized electromagnet accomplishes the same task without needing to be moved; from a fixed position within a socket, it is energized, and the magnetic properties it inherits closes ( or opens ) a switch.
A Hall effect sensor exploits forces that are imparted upon charges moving through a magnetic field ( B ):
In regard to the movement of negative charge, the Left-Hand Rule is used to determine the orientation of a circular magnetic field around a current-carrying wire. Simply point the thumb of the left hand in the direction of current flow, then curve the remaining four fingers inward. In the diagram above, a field created by the wire would go against the magnet’s B-field on one of its sides, and its direction would coincide with that of the magnet on the opposing side. In the region where field cancellation occurs, the electrons congregate. This leaves a potential difference ( V ) across the wire. The stronger the current or magnetic field, the stronger the wire-deflection within the Hall sensor. Hall Effect sensors are also inexpensive, and they are useful in detecting the presence of stray magnetic fields in sensitive electrical circuits.
RENAISSANCE PHYSICS 