1. Motors and Generators
Physics 12 Adv

2. DC Electric Motor
If a current carrying coil is placed in a magnetic field, it will experience torque
This will cause it to rotate so that it no longer experiences a force that causes it to rotate
At this point, a split ring commutator will reverse the current direction so that the coil will continue to rotate

3. AC Electric Motor
The design of the AC motor is similar to the DC motor except the split-ring commutator is replaced by two slip-ring commutators
As AC current is alternating, the voltage source will reverse the current in the loop so the split-ring commutator is no longer required

4. DC Motor – Step by Step

5. Motor Questions
How could you increase or decrease the frequency of rotation of a motor?
How could you increase the rate of energy output for a given motor (assuming no changes in the actual construction)?

6. Lenz’s Law
When a conductor interacts with a magnetic field, there must be an induced current that opposes the interaction, because of the law of conservation of energy

7. Eddy Currents
These are an application of Lenz’s law and can be used in balances in order decrease the time it takes to come to rest

8. Generator Effect
With a motor, a moving charge in a magnetic field results in a force on the wire
In a similar manner, moving a magnet past a conducting wire will result in a force on the charge carriers (i.e. a current)

9. Right Hand Rule for Generator Effect
The fingers point in the direction of the magnetic field
The thumb points in the direction of motion of the wire
The palm shows the direction of the emf (electromotive force)

10. DC Generator
A DC generator is essentially a DC motor that is designed to convert motion to electricity instead of vice versa
The voltage will alternate between a max and zero

11. AC Generator
The difference with an AC generator is that in does not require a split-ring commutator but instead uses two slip-ring commuators
This is because the direction of current in an AC device alternates (positive/negative)

12. Electromotive Force The emf is a function of: Magnetic Field (B)
Length of wire (L)
Speed of wire (v)

13. Section Review
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