Magnetism and Electromagnetism Notes

More than 2000 years ago, the Greeks discovered a natural magnet mineral called magnetite.
In the 12th century, Chinese sailors used magnetite to create compasses for improved navigation.
Magnetism refers to the properties and interactions of magnets.
Magnetic forces either repel or attract each other.
The strength of the force between two magnets:
- Increases as magnets move closer together.
- Decreases as magnets move farther apart.
Magnetic Field:
- A region of space that surrounds a magnet.
- Exerts a force on other magnets and objects made of magnetic materials.

Magnetic field lines illustrate the magnetic field around magnets.
The closer together the magnetic field lines are, the stronger the magnetic field is at that point.

Magnetic fields are strongest at the ends of a bar magnet.
Regions of a magnet that exert the strongest force are called magnetic poles.
All magnets have a north and south pole.
Like poles repel, and opposite poles attract.
When two magnets are brought close together, their magnetic fields combine to produce a new magnetic field.
Magnetic field lines always point away from the north pole and towards the south pole.

A compass can help determine direction because the needle's north pole points to a location near Earth's geographic north pole.
Earth's geographic north pole is the northernmost point on Earth.
A compass needle will align with Earth's magnetic field lines.
Earth's magnetic field is not very strong.

Examples of magnetic materials: Iron, cobalt, and nickel.
Every atom contains electrons, which have magnetic properties.
In most elements, the magnetic properties of electrons cancel out.
In magnetic elements, these magnetic properties do not cancel out, and each atom behaves like a small magnet with its own magnetic field and north and south poles.

In magnetic materials like iron, the magnetic field created by each atom exerts a force on other nearby atoms.
These forces cause large groups of neighboring atoms to align.
This means that almost all north magnetic poles in the group point in the same direction.
Magnetic Domain: A large group of atoms with their magnetic poles lined up in the same direction.

Magnetism and electric current are related.
Electromagnetism: The interaction between magnets and electric charges.
Electromagnetic Force: Produced by the interaction of electric force and magnetic force; a fundamental force like gravity.

A single wire carrying electric current that is wrapped into a cylinder-shaped coil.
This makes a magnetic field stronger.

A solenoid wrapped around an iron core.
These are temporary but strong magnets.
The magnetic field exists only when there is a current flowing through it.
Useful because you can control how they act by changing the electric current flowing through the solenoid.
Electric energy is changed into mechanical energy.
Electromagnets make mechanical energy to do the work in many devices.

A machine that changes electrical energy into mechanical energy (e.g., a fan or airplane).
Any machine that changes electric energy into kinetic energy is a motor.
A motor contains a permanent magnet and an electromagnet connected to an electric source.

Use electromagnetic induction to change mechanical energy into electrical energy.
Electromagnetic induction: The making of a current by a changing magnetic field.
Electric generators are used in cars (called an alternator) to provide electrical energy for lights and spark plugs.

Electric power plants produce most of the electrical energy.
In a power plant, the coils don't rotate; the permanent magnets do.
Mechanical energy rotates the magnet, and electrical current is produced in the coil.
The magnets are connected to a turbine, which is a large windmill-like wheel.
The turbine rotates when it is pushed by steam, water, or wind, and the rotating magnets produce the electric current in the wire coils.

When a power outage occurs, some electric devices, like an alarm clock, use batteries as a backup source of electrical energy.
Direct Current (DC): Electric current that is always in one direction through a wire.
Alternating Current (AC): Electric current that reverses the direction in a regular pattern.
In America, the alternating current in a wall socket has a frequency of 60 Hz and an average voltage of 120 V.

To reduce the voltage without changing the amount of electrical energy, devices use transformers.
Transformer: A device that increases or decreases the voltage of an alternating current.
A transformer is made of a primary coil and a secondary coil.