Physics – 4.5.3 Magnetic effect of a current | e-Consult

Relays: A relay uses the magnetic effect of a current to control a larger current. A coil of wire is placed around an iron core. When a small current flows through the coil, it creates a magnetic field. This magnetic field then attracts a movable armature, which is connected to a set of contacts. The movement of the armature closes or opens these contacts, thereby controlling a larger current in a separate circuit. The small current in the relay coil acts as a switch to control the larger current.

Example Applications: Relays are used extensively in electronic devices and electrical systems. Examples include:

• Household appliances: In washing machines, refrigerators, and ovens, relays control the power supply to different components.
• Automotive systems: Relays are used in car starting systems, headlights, and horn circuits.
• Control systems: In industrial automation, relays are used to control motors, pumps, and other machinery.
• Telecommunications: Relays were historically used in telephone switching systems.

Loudspeakers: A loudspeaker uses the magnetic effect of a current to convert electrical energy into sound energy. A coil of wire (the voice coil) is attached to a cone. This coil is placed within a magnetic field created by a permanent magnet. When an alternating current (AC) flows through the voice coil, it creates a varying magnetic field. This varying magnetic field interacts with the permanent magnet, causing the coil and cone to vibrate. These vibrations create sound waves that we hear.

Example Applications: Loudspeakers are ubiquitous in audio systems.

• Audio systems: Used in home stereo systems, car audio, and public address systems.
• Musical instruments: Electric guitars and keyboards use loudspeakers to amplify the sound.
• Communication systems: Used in telephones, radios, and television sets.
• Alarms: Used to produce audible warnings in security systems.