Suspicions had existed for a long time that there was some link between electricity and magnetism before Christian Oersted showed that an electric current could deflect the compass needle of a magnet.
Later in 1821, Andrea Ampere built the first electromagnet, using an electric current to produce a magnetic field.
In England, the scientist Michael Faraday built the first electric motor, also in 1821. Electric motors use electric currents to produce motion. He illustrated magnetic fields as lines of flux exiting the north pole of a magnet and entering into the south pole. His idea was later used by many scientists to illustrate many force fields. The field lines typically have arrows on them to indicate the direction of the force on a particle.
Faraday also thought it should be possible to use an electric motor in reverse – that is, to use motion to produce an electric current. He had to show that a magnetic field could induce motion in a coil (electromagnetic induction) and succeeded in building the first generator in 1831. He also built the first transformer allowing voltages to be transformed up and down.
For most people however, electricity was just a curiosity until devices started to appear that needed electricity to function. The telegraph appeared in 1837 and the telephone in 1866. The first practical electric light bulb appeared in 1879, then new electrical devices started to flo and enter the home.
JJ Thompson discovered the electron in 1897. He demonstrated that electric current was really a flow of negatively charged electrons, and that a beam of electrons could be bent by a magnetic field.
The first practical vacuum tube was invented in 1904. This could be used as an electronic switch and meant the first electronic devices could be built. Radio and television sets wet orginally built with vacuum tubes, and during the was, the first computers were built in the utmost secrecy to break German codes.
In 1865 electricity and magnetism were shown be different aspects of the same force – the electromagnetic force, by a Scottish scientist, James Clerk Maxwell. Maxwell predicted the existence of electromagnetic waves, which were discovered by Heinrich Hertz in 1888. These waves move throughout space as a couple pair of oscillating electric and magnetic fields. A changing electric field produces a changing magnetic field and a changing magnetic field produces a changing electric field.