Unit 6Magnetism

Chapter 8Pages 226-255

Magnets

• Two magnets exert a force on each other• The magnetic force is the interaction you feel

before the two magnets even touch each other

• The strength of this force increases as you move the magnets closer together

• The magnetic field exerts the magnetic force• Each magnet has a north and south pole• This is where the magnetic force is the

strongest• Like poles repel• Opposite poles attract

Earth’s Magnetic Field• On a compass, the needle points to

geographic North• This is because earth’s south magnetic pole is

located in Canada• So opposites attract• The north on the compass to the “south” in

Canada

Magnetic Domains

• Groups of atoms with aligned magnetic poles are called magnetic domains

• This allows the object to behave like a magnet with north and south poles

• Ex: Placing a magnet against an iron nail will cause all the atoms to orient themselves in the same direction and temporarily cause the nail to act as a magnet

Electric Current and Magnetism

• Moving charges produce magnetic fields• The direction of the field depends on the

direction of the current• The strength of the field depends on the

amount of current flowing through the wire

Electromagnets

• An electromagnet is a temporary magnet made by placing iron inside a current carrying coil of wire

• The more the wire is coiled around the iron, it causes a stronger magnetic field

• When current flows through the electromagnet it moves toward or away from another magnet, converting electric energy into mechanical energy to do work

• Ex: stereo speakers contain electromagnets

Galvanometers

• Gauges on your dashboard of your car are galvanometers

• They measure the current being sent from sensors which in turn register the amount of gasoline you have left

Electric Motors

• An electric motor is a device that changes electrical energy into mechanical energy

• Like galvanometers, electric motors use an electromagnet

• The movement of the current is constantly switched back and forth to maintain the rotation of the coil

• Some motors use a commutator to do this, others use household alternating current

• Electric motors are most useful if their rotation speed is controlled

• Today’s motors are smaller, more powerful, and more efficient than the first ones developed in the late 1800s

Electric Generators

• Electromagnetic induction is caused when a magnet is moved through a wire coil or rotating a coil of wire through a magnetic field

• This is how generators produce electricity• Again, the current flow must constantly switch

directions in order for the coil to turn continuously

Types of Generators

• In your car, it is called an alternator• Power plants use generators to allow

electricity to reach your home• Here the electromagnets are connected to a

turbine pushed by either water, wind, or steam

Direct and Alternating Currents

• A battery produces a direct current, which flows in only one direction of a wire

• Generators produce alternating current, which reverses the direction of current flow in a regular way

Transformers

• Alternating current traveling through power lines is a high voltage so as to reduce the amount of energy lost as heat

• A transformer can either decrease the voltage (step down) or increase it (step up)

• Step up transformers have more turns of wire in the secondary coil than in the primary coil