Bar magnet induces current in a coil, shown on galvanometer.

Bar magnet induces current in a coil, shown on galvanometer. A changing magnetic field cutting across a coil of wire induces an electric current. In 'A', a cylindrical bar magnet is thrust into a tall narrow coil which is hooked to a projection galvanometer. The induced current causes the needle to swing full scale in both directions. In 'B', the narrow coil is placed inside a coil of larger diameter. A 6 volt D.C. battery and key switch are hooked to the larger coil. When the switch is pressed, the surge of magnetic field from the larger coil cuts the narrow coil. A current surge is registered when the switch is pressed or released, smaller than in 'A'. In 'C', a soft iron cylindrical core is inserted into the narrow coil. When the switch is pressed or released, a much larger current swing is registered than in 'B'. Other cores can be inserted: a bundle of iron wires, a brass rod, or a lucite rod.