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Electromagnetic Induction Electricity is induced in the coil when the number of magnetic field lines inside the coil changes In order for electromagnetic induction to occur, the number of magnetic field lines inside the loop must change. How can this be done? There are 3 ways to change the number of magnetic field lines inside the loop. • Change the magnetic field, B • Change the area of the loop (convert to a circle) • Rotate the loop Electromagnetic induction occurs when the loop area in a magnetic field changes (quickly). The magnetic force (F) due to the induced current (I) opposes the motion of the rod to the right. If this didn’t happen, we would have a perpetual motion machine. Electromagnetic induction occurs when the loop in a magnetic field is rotated (quickly). THE BIG PICTURE Electricity is induced whenever the number of magnetic field lines inside the loop of wire is quickly changed. The number of magnetic field lines inside the wire loop changes when the loop is rotated. The faster this change occurs, the larger the induced voltage. Generator Simulation Generator Motor Input loop rotation electricity Output electricity loop rotation Once a generator is producing electricity, it has a motor effect that tries to spin the loop in the opposite direction of the input. Once a motor has loops rotating, it has a generator effect that induces electricity in the opposite direction of the input. The guitar string is magnetized by the pickup magnet. When the string vibrates, the wire coil experiences a changing magnetic field. Electricity is produced via electromagnetic induction. In a microphone, the magnetic field inside the vibrating coil rapidly changes. Electromagnetic induction occurs. Loudspeakers and microphones have the same parts. Microphone Loudspeaker Input sound electricity Output electricity sound In a phono cartridge, when the stylus passes through the grooves of a record it will vibrate. This causes the magnet inside the coil to also vibrate. Since there is now a rapidly changing magnetic field inside the coil, electromagnetic induction occurs. Transformers Transformer - a device for increasing or decreasing voltage through electromagnetic induction. Power in equals power out If the voltage increases, the current must decrease.