1. A Galvanometer
2. A bar magnet
3. Some wire
4. A cardboard tube
Step 1: Wind the wire around the tube as many as 50 times
Step 2: Connect the ends of the wire to the galvanometer
Step 3: Take your bar magnet and move it back and forth through the coil
Does the galvanometer show electric current?
While Oersted's surprising discovery of electromagnetism paved the way for more practical applications of electricity, it was Michael Faraday who gave us the key to the practical generation of electricity: electromagnetic induction. Faraday discovered that a voltage would be generated across a length of wire if that wire was exposed to a perpendicular magnetic field flux of changing intensity.
An easy way to create a magnetic field of changing intensity is to move a permanent magnet next to a wire or coil of wire. Remember: the magnetic field must increase or decrease in intensity perpendicular to the wire (so that the lines of flux "cut across" the conductor), or else no voltage will be induced:
A changing magnetic flux induces a current into a coil.
Demo 1: As the magnet is moved in, the magnetic flux through the solenoid changes and an induced current appears (Faraday's law). The faster the magnet the higher the induced current. If the solenoid is approached first with the other magnetic pole, the direction of the induced current changes. When the magnet is moved away from the solenoid the direction of the current changes again.
Demo 2: Same as above but using a different coil and a digital multimeter.
Demo 3: The set up consists of two solenoids: one large one connected in a simple circuit and a second, smaller one, connected to an ammeter. When the switch is closed, a DC current is established in the circuit and a steady magnetic field is produced in the large solenoid. There is no induced current in the small solenoid as the magnetic flux through it does not change. However, when the switch is switched on or off, an induced current is produced. This is because for a short period of time the current changes and therefore the magnetic field produced by the large solenoid changes as well - hence an induced current in the small solenoid.
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