Electricity and magnetism
Electricity and magnetism are closely intertwined. Two of the greatest discoveries of the 19th century were that a wire carrying an electric current acts like a magnet and that a change of magnetism can make current flow. (Putting the two together, this also means that a changing current in one wire can make current flow in another.) These discoveries have had an enormous effect on everyday life. They have allowed us to build generators that can convert the energy in fuels like coal or oil into abundant electric power, using wires with currents flowing in them as magnets and whirling them past other wires to create even bigger currents. Just a little of this power goes into electronic devices. By exploiting the intimate relationship between magnetism and electricity, electronic devices can make music, pictures, or even radio waves.