Modern magnetism

Augustin Jean Fresnel, best known for his work with light, mentioned in a letter to Ampère that the electric currents responsible for magnetic forces might operate at microscopic lengths.

At the start of the twentieth century another French physicist, Pierre Weiss, developed his theory of magnetism, which began to describe magnetic interactions at the microscopic scale. With the advent of quantum mechanics, magnetic interactions became better understood.

Building on these new principles, magnetic recording systems developed at the end of the nineteenth century were improved and the consequent development of magnetic tape eventually paved the way for the audio tape recorder in the middle of the twentieth century.

Today, magnets are pervasive in daily life:

• Cars contain magnets in starter motors, electric windows, door locking systems, electronic relays and alternators.

• Kitchens have magnetic motors in refrigerators, microwave ovens, washing machines and tumble dryers.

• Entertainment systems such as video recorders, CD and DVD players, audio tape recorders and minidisc players all contain motors. These motors contain magnets.

• Televisions and monitors use magnets to deflect and position the electron beam used to create an image, as well as high-voltage electromagnets to degauss the tube. Degaussing eliminates apparent colouring problems with the display tubes in these devices.

• Electric bells in telephones, alarms and doorbells contain magnetic ringers.

• Medical applications include the use of magnetic fluids in eye surgery and drug delivery, as guides in keyhole surgery, prosthetics, cancer therapy and magnetic resonance imaging.

Magnets can also be found on the reverse side of credit cards, in cooling fans, power station generators and audio speakers. One of the fastest-developing areas in magnetism is in the area of data storage in computers, particularly hard disk drives.