Electromagnet

What it is

A coil of wire around an iron core that becomes magnetised when current flows through it, able to lift loads heavier than itself. It is the active component of the telegraph, the relay, the motor and the bell.

Sturgeon presented it in 1825; Henry, in Albany (New York), insulated the wire with silk and achieved electromagnets capable of lifting hundreds of kilograms in 1831, essential for the telegraph.

What it led to

• The practical electric telegraph
• The relay and electromechanical logic
• Motors and generators
• Bells, locks and magnetic separation

Built on

• Voltaic pile1800
• Ørsted's effect: electric current deflects a compass1820
• Ampère's law and electrodynamics1820-1827
• Ørsted's discovery (1820)
• Ampère's solenoid

Made possible

• Electric motor1821-1834
• Electromagnetic induction1831
• Electric generator and self-excited dynamo1832-1867
• Self-inductance (Joseph Henry)1830-1832
• Electric telegraph1837
• Electric clock and electrochemical fax1841-1843
• Telephone1876
• Silicon electrical steelc. 1899-1903
• Cyclotron1930–1932
• Relay

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