1. Electricity and Magnetism
Section 8.2

2. Moving charges and magnetic fields
Moving charges, like those in an electric current, produce magnetic fields
The magnetic field around a current-carrying wire forms a circular pattern about the wire
The direction of the field depends on the direction of the current

3. Moving charges and magnetic fields
The strength of the magnetic field depends on the amount of current flowing in the wire
Electromagnet- a temporary magnet made by placing a piece of iron inside a current carrying coil of wire

4. Electromagnets
Magnetic field is present only when current is flowing in the wire coil
Increase strength of the magnetic field by adding coils to the wire or increasing the current flowing through the wire
Magnetic properties of electromagnets can be controlled by changing the electric current flowing through the wire coil
Converts electrical energy into mechanical energy to do work- like speakers!

5. Galvanometer
Galvanometer- a device that uses an electromagnet to measure electric current
Examples: gas indicator, engine light, oil temperature
Current changes as temperature changes, needle is connected to an electromagnet, which is suspended so it can rotate between the poles of a permanent fixed magnet
When current flows through the coil, the electromagnet rotates

6. Electric motor
Electric motor- a device that changes electrical energy into mechanical energy
Contains an electromagnet that is free to rotate between the poles of a permanent fixed magnet
The coil in the electromagnet is connected to a source of electric current (battery, power outlet)

7. Electric motor
When a current flows through the electromagnet, a magnetic field is produced in the coil
Changing the direction of the current causes the coil in the electric motor of keep rotating
Rotation speed of electric motors can be controlled
Vary the amount of current flowing through the coil

8. Electric motors
When more current flows through the coil, the electromagnet’s magnetic field becomes stronger
The magnetic force between the coil and the permanent magnet increases, and the coil turns faster
Commutators- reverse current in the coil- for DC power sources.
AC reverses direction 120 times a second, so they don’t need commutators
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