# DC motor and AC generator's output

1. Sep 27, 2012

### sgstudent

To increase a DC generator's turning effect, we increase the number of turns of the coil. How does this increase the turning effect? Will it concentrate the field lines or will the force acted on each coil be added to each other to increase the force on one armature? I think both happens because someone on the forum a while ago told me that the magnetic field lines would be concentrated as well.

To increase a AC generator's emf, we increase the frequency of the turning. Will the explanation for the increase be: The speed of rotation would be increase as the period of the rotation is decreased. Since the speed is increased, the rate of change of magnetic flux linkage is increased hence, the emf will be increased.

Also, by increasing the number of turns the coils, will the explanation also be: Since the number of turns of the coils increases, the rate of change in magnetic flux linkage is increased as well as there is a greater number of coils to link the circuit with the magnetic field lines. With the increased rate of change of magnetic flux linkage, the emf induced will be greater.

With these two examples, when we use Fleming's Right-hand rule, the motion (thumb) refers to the speed of rotation? Since the speed is the one that determines the rate of change of magnetic flux linkage which in turns affect the induced emf.

Thanks for the help!

2. Sep 29, 2012

### Philip Wood

The start of your post is puzzling. When a generator is driving a current through a load it produces a torque in the opposite direction to the direct in which it (its armature) is being turned. Is this torque the 'turning effect' to which you are referring? If so, it will increase with the number of turns, n, on the coil, because of the increased emf, which will drive a greater current through the load, and therefore through the coil itself. What's more, increasing n will also increase the torque per unit current, so the torque will be proportional to n2 (provided the load resistor is large, so we can forget changes in the coil's resistance due to adding more turns).

Last edited: Sep 30, 2012