Q.Describe Oersted's experiment in brief and state what it demonstrated about the relationship between electricity and magnetism.

In 1820, Hans Christian Oersted discovered that a current-carrying wire deflects a nearby compass needle, and that reversing the current reverses the deflection -- proof that a steady current is itself a source of magnetic field, unifying electricity and magnetism as electromagnetism. The resulting field forms concentric circles around a straight wire (weakening as $1/r$ with distance) and a more complex, nearly-uniform-near-the-centre pattern around a circular coil. Its direction is read off with either of two equivalent rules: the right hand thumb rule (thumb along the current, curled fingers give the field) or Maxwell's right hand cork screw rule (a right-handed screw advancing along the current turns in the direction of the field) -- both are used constantly throughout the rest of the unit to fix the direction of every derived field and force.