Video narration
How can a bicycle light shine when there's no battery in the wheel? As the wheel turns, the dynamo changes magnetic conditions and sends current to the lamp. The same surprise appears with two coils: one, a powered solenoid, sits near an unpowered coil connected to a galvanometer. Switch the solenoid on or off, move it toward or away, or change its current, and the meter deflects-then returns toward zero. Here's the turn: the battery is not feeding the second coil. A changing magnetic field through that coil creates an induced current. This is electromagnetic induction, described by Faraday's law. Change the field faster, and the galvanometer deflects more. To find the current's direction, use Fleming's right-hand rule, when the three directions are perpendicular: thumb for the conductor's motion, index finger for the magnetic field, and middle finger for the induced current. So, can a coil make current without its own battery? Yes-if the magnetic field through it is changing, just like the moving dynamo.