Magnets, coils and galvanometers: function and handling

The magnet supplies a magnetic field. The coil links some of that field, and a change in linked flux induces an electromotive force. In a closed conducting circuit, a galvanometer can indicate the resulting current. These are different roles: a current indication is not automatically a voltage measurement.

This guide covers supplied parts in a magnet-and-coil investigation with no external power. No battery or external power supply is connected. The trainer chooses compatible coil, leads, meter range and magnet.

Know what the meter indicates

IOP's magnet-and-coil activity explicitly distinguishes generated emf from the current observed through a galvanometer. The size of a deflection depends on the circuit and instrument response, not only the induced emf.

Record the meter's starting indication, its lead connections and which pole moves through which end of the coil. Reversing connections changes the meaning of left and right deflections. There is no universal leftward response for an entering north pole.

Do not treat a scale division as a voltage unit without an appropriate calibrated method. A larger deflection from a quicker hand movement is a qualitative comparison, not proof of an exact proportional change in emf.

Change flux without striking the apparatus

A stationary magnet can provide a strong field without maintaining a changing flux through a stationary coil. Relative motion along the prescribed path changes the linked flux; the path and pole orientation therefore matter.

Use the assigned clearance and support. Do not drive the magnet against a coil, meter or fitting to make a larger response. The induction practical develops the controlled observations.

Keep external power out of this investigation

Prepared leads and the actual meter range must be checked before use. Do not add a battery to enlarge a small indication; it would create a different circuit and could overload sensitive equipment.