Magnetism from Electric Currents

• Hans Christian Oersted found that magnetism is produced by moving electric charges.
• Electric currents produce magnetic fields.
• The magnetic field of a coil of wire resembles that of a bar magnet.
• A solenoid is a coil of wire with an electric current in it.
• In a solenoid, the magnetic field of each loop of wire adds to the strength of the magnetic field of the loop next to it.
• More loops or more current can create a stronger magnetic field.
• An electromagnet is a coil that has a soft iron core and that acts as a magnet when an electric current is in the coil.
• Magnetism can be caused by moving charges.
• Negatively charged electrons moving around the nuclei of all atoms make magnetic fields.
• Atomic nuclei also have magnetic fields because protons move within the nucleus.
• Each electron has a property called electron spin, which also produces a tiny magnetic field.
• Magnetic atoms rotate to align with the magnetic fields of nearby atoms creating small regions within the material called domains.

Electromagnetic Devices

• Galvanometers detect current.
• A galvanometer is an instrument that detects, measures, and determines the direction of a small electric current.
• Electric motors convert electrical energy to mechanical energy.
• A device called a commutator is used to make the current change direction every time the flat coil makes a half revolution.
• Devices called brushes connect the wires to the commutator.
• Stereo speakers use magnetic force to produce sound.
• When the direction of the current in the coil of wire changes, the paper cone attached to the coil moves, producing sound waves.