12-03-2012, 02:36 PM
Electric Generators
[attachment=18213]
Convert mechanical energy into electrical energy
A direct result of Faraday’s work on induction
Basically, the inverse of the electric motor which converts electrical energy to mechanical energy
AC Generator
We saw earlier that we can consider Faraday’s Law or we can just calculate the forces on the individual electrons making up the current. We’ll do the latter here.
All the action takes place in the wire segments ab and cd.
The forces on electrons in ad and bc are sideways the the electrons don’t move along the wire due to these forces.
DC Generators
Replace the brushes with slip rings and you get a DC generator. Notice the voltage is not steady. The coil is shown at the top and bottom of the shaft.
If we increase the number of turns and arrange them as shown, we can smooth out the variations in voltage.
In the old days, autos used DC generators to recharge the battery.
Counter EMF
In this DC motor, the current produces a torque. If you keep applying a torque, the angular velocity continues to increase! However, as the coil turns, the magnetic flux changes and an EMF is produced. By Lenz’s Law, this opposes the change. So an equilibrium speed is obtained. See examples in the textbook.
In a generator when current flows to an external load, the current in the coils experiences a torque (just like in a motor).
This torque opposes the mechanical motion causing the induced current.
[attachment=18213]
Convert mechanical energy into electrical energy
A direct result of Faraday’s work on induction
Basically, the inverse of the electric motor which converts electrical energy to mechanical energy
AC Generator
We saw earlier that we can consider Faraday’s Law or we can just calculate the forces on the individual electrons making up the current. We’ll do the latter here.
All the action takes place in the wire segments ab and cd.
The forces on electrons in ad and bc are sideways the the electrons don’t move along the wire due to these forces.
DC Generators
Replace the brushes with slip rings and you get a DC generator. Notice the voltage is not steady. The coil is shown at the top and bottom of the shaft.
If we increase the number of turns and arrange them as shown, we can smooth out the variations in voltage.
In the old days, autos used DC generators to recharge the battery.
Counter EMF
In this DC motor, the current produces a torque. If you keep applying a torque, the angular velocity continues to increase! However, as the coil turns, the magnetic flux changes and an EMF is produced. By Lenz’s Law, this opposes the change. So an equilibrium speed is obtained. See examples in the textbook.
In a generator when current flows to an external load, the current in the coils experiences a torque (just like in a motor).
This torque opposes the mechanical motion causing the induced current.
