Summary
Highlights
Electromagnetic induction can be demonstrated by forming a coil from insulated copper wire and connecting its ends to a galvanometer. When a magnet is moved towards or away from the solenoid, the galvanometer deflects, indicating current flow. The direction and magnitude of the current depend on the magnet's motion, polarity, and speed, as well as the coil's properties.
Faraday observed that current only flows when there is relative motion between the coil and the magnet. The direction of current reverses with the direction of motion or the magnet's polarity. The induced current can be increased by using a stronger magnet, increasing the magnet's velocity, or increasing the coil's area or number of turns.
According to Faraday, when there's no relative motion, the magnetic flux within the coil remains constant, and no current is induced. However, when the magnet moves, the magnetic flux changes, inducing an electromotive force (EMF) in the coil. If the circuit is complete, this EMF causes current to flow.
Faraday formulated two laws: First, an EMF is induced whenever there is a change in the magnetic flux linked with a coil. Second, the magnitude of the induced EMF is directly proportional to the rate of change of the magnetic flux. The direction of the induced EMF depends on whether the magnetic flux is increasing or decreasing.
John Ambrose Fleming developed rules to determine the direction of motion or induced current. While the left-hand rule is for electric motors, the right-hand rule is for generators. In Fleming's right-hand rule, the thumb indicates the direction of conductor movement, the forefinger indicates the magnetic field direction, and the middle finger indicates the direction of the induced current.
Lenz's law states that the direction of the induced EMF always opposes the cause that produces it. This law aligns with Newton's third law of motion (action-reaction) and the law of conservation of energy, meaning energy is neither created nor destroyed. Lenz's law is based on Faraday's law of induction, explaining that the polarity of the induced EMF creates a current whose magnetic field counteracts the change in flux.