(a) What is meant by the magnetic field produced by an electric current?
(b) With the help of a neat, labelled sketch of the field lines, describe how the direction of the magnetic field surrounding a long straight current-carrying conductor can be identified experimentally.
(c) Explain qualitatively how the magnitude of this magnetic field depends on (i) the current in the conductor and (ii) the perpendicular distance of the observation point from the conductor.