here's my 2 cents:
the galvanometer:
the galvanometer consists of a coil wrapped around a soft iron core, with an attached needle with recoil spring, radial magnets and a reading meter.
when current passes through the coil, it becomes a current carrying conductor, and undergoes the motor effect since it is under the influence of a radial magnetic field (from the magnets). the force applied to the coil from the motor effect causes the coil to rotate, and therefore, causes the needle to rotate/move as well, to indicate a reading on the meter. the recoil spring undergoes increased tension as the needle moves. the meter can therefore be calibrated for accurate readings.
When there is no current passing through the coil, the needle will return back to "0" because of the release of elastic potential energy from the recoil spring. the radial magnetic field is to provide a constant maximum torque, again, for accurate readings on the meter.
loud speaker to come!