Science Ch. 8
Example of direct current
battery
Step- up transformer
increases voltage, second coil has more turns than 1st coil
Electric current creates
magnetic fields
Where is the magnetic force the greatest in a horseshoe magnet?
near the poles
How can you force an electromagnet to rotate?
with mechanical energy
Generator
Device that produces electric current by rotating a coil of wire in a magnetic field
Two ways a magnet can lose their magnetic behavior
Heating or strike with a hammer
How does a generator work?
1. an electromagnet is placed between the poles of a permanent magnet 2. The coil rotates by mechanical energy 3. Electric current produced as coil turns through magnetic field
How many years ago did greeks discover deposits of a mineral that was a natural magnet?
2000 years ago
Where is the electromagnet on the motor?
Coil
Direct current
Current that flows in only one direction through a wire
Step- down
Decreases voltage, 2nd coil has fewer turns of wire than 1st coil
Galvanometer
Device that uses an electromagnet to measure an electric current
Magnetic field
Exerts a force on magnetic objects represented by field lines.
Turbine
Large wheel that rotates when pushed by steam, wind, or water and that provides mechanical energy to a generator
Where is the permanent magnet on the motor?
Magnet
Three magnetic materials
Nickel, Cobalt, and Iron
Magnetism
Refers to the properties and interactions of magnets
Magnetic pole
Region where a magnet's magnetic force is strongest
Electromagnet
Temporary magnet made by wrapping a wire coil carrying a current around an iron core.
Electromagnetic induction
The process by which moving a wire through a magnetic field produces an electric current
Solenoid
a wire wrapped into a coil
Where is the magnetic field lines the strongest?
at the poles
Where is a voltage source on the motor?
battery
Magnetic domains
groups of atoms in magnetic materials can align their magnetic poles
2 ways to increase the magnetic force?
increase the number of coils or current
Temporary magnets
magnet only when current flowing through a wire.
example of alternating current
outlets
Like magnetic poles always___ each other
repel
The north pole of one magnet will be attracted to the _____ of another magnet
south pole
How is the magnetism lost in a coil?
stopping or starting a current
Alternating current
When a current in a circuit reverses its direction in a regular pattern
Magnetite
a mineral that attracts pieces of iron on it
Explain how a compass works
A compass's needle is attracted to earth's north pole and it always points to earth's magnetic south pole. The needle is a magnet and it attracts to the north pole. The needle of a compass is a freely rotating magnet. The painted end is the south (magnetic) pole of the needle which is attracted by the weak magnetic field of the earth to align itself in a northerly direction (opposite poles attract so the south pole of the compass is attracted to the north pole of the earth's magnetic field). The area to which it points is called the North Magnetic Pole which is close to, but not exactly at geographic North Pole.
Transformer
A device used to increase or decrease the voltage of current in some motors
Electric motor
A machine that changes electrical energy to mechanical energy, used to do work
Permanent Magnet
Magnetize material by placing in a strong magnetic field
What is theorized to cause the earth's magnetic field?
Molten iron and nickel in earths core produce earth's magnetic field
