Electricity and Magnetism Section 8.2

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

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 http://www.howstuffworks.com/electromagnet.htm http://ithacasciencezone.com/midscizone/physical/p04magnetism/magnetism/slide4.htm

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!

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 http://www.hometrainingtools.com/articles/homemade-galvanometer.html

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)

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

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 Extra info: http://www.physclips.unsw.edu.au/jw/electricmotors.html