Electromagnetism(S8P5 b, c) Physical Science Candace Black Spring, 2010
Electric Current and Magnetism • Electric current produces a magnetic field. • The relationship between electricity and magnetism is called electromagnetism Can you identify the 3 necessary parts of a circuit?
Solenoids 3 characteristics of magnetic field produced by current: 1. Can be turned on or off. 2. Direction can be reversed. 3. Strength can be changed. A coil of wire with a current is called a solenoid.
Electromagnets • A solenoid with a ferromagnetic core is called and electromagnet. • Magnetic field is produced by both the current in the wire and the magnetized core. • A strong magnet that can be turned on and off. • Increase strength by: 1. Increasing current 2. Add more loops 3. Place coils closer together 4. Use stronger ferromagnetic material as core.
Uses of Electromagnets • Audiotapes, videotapes, computer hard drives, credit cards… • Doorbell • Fire doors…(be able to explain how these work in our school) • To lift heavy objects such as junk cars, metal containers such as are used in shipping, etc.
Electric Motors A device that uses an electric current to turn an axle. Transforms electrical energy into mechanical energy.
In your notes, write at least 3 things that you can think of that use motors.
Induction of Current • Electric current is induced in a conductor when the conductor moves through a magnetic field. • Generating an electric current from the motion of a conductor through a magnetic field is called electromagnetic induction. • Current that is generated in this way is called induced current.
A current consisting of charges that flow in one direction only is called a direct current or DC. Example: battery operated items; charges flow from positive end through circuit back to negative end. A current that flows back and forth in a circuit is called an alternating current or AC. Example: homes, buildings, schools, Advantage: voltage can be raised or lowered; higher voltages can travel over longer distances (from power plant); then can be lowered for everyday use (in our homes). Induced Currents
Generators • An electric generator is a device that transforms mechanical energy into electrical energy. • A generator uses motion in a magnetic field to produce an electric current. • Electric motors use and electric current in a magnetic field to produce motion. • Generators are used in power plants with turbines acting as the crank. Be able to compare/contrast generators and motors.
Transformers • A transformer is a device that increases or decreases voltage. (voltage is…?) • Consists of 2 separate coils of insulated wire wrapped around an iron core. • Two types of transformers are: 1. step-up transformer —increases voltage. 2. step-down transformer —decreases voltage.
??????????? What are your questions?