Untitled Flashcards Set

A magnet is any object that attracts iron, or iron- like metals.

All magnets have two poles, or ends of the magnet, where the force of the magnet is strongest.  We call these poles North (N) and South (S).

If you break a magnet into pieces, each piece will have both a North and a South pole.  It’s not possible to have a single magnetic pole.

The force of attraction or repulsion between two magnets is called their magnetic force:

• Like poles repel each other (N with N, or S with S)

• Unlike poles attract each other (N with S)

All magnets are surrounded by a magnetic field.  This means that magnets can attract and repel each other (or magnetic materials) without having to physically touch each other.

When you combine magnetic fields, they form a stronger magnetic field.  This can be a field of attraction or repulsion, depending on the poles you bring together.

The Earth is surrounded by a magnetic field, as well.  Compass needles are permanent magnets that spin around their middles in order to determine direction, since they will respond to the earth’s magnetic field.

• The Earth’s Geographic North Pole (over Alaska and Canada) is actually a Magnetic South pole.  That’s why the North pole of a compass points to the North pole of the Earth.

Materials that can be attracted to a magnet, such as an iron nail, or steel paperclip, are called magnetic materials.  They contain ferromagnetic elements, such as:

• Iron

• Nickel

• Cobalt

• Steel is not an element, but contains iron, and, as such, is ferromagnetic.

What makes a magnet a magnet?  All atoms have magnetic north and south poles because they contain electrons.  We call these magnetic poles of atoms magnetic domains:

• In a permanent nonmagnet, the magnetic domains are askew (all jumbled up).  Their magnetic fields cancel each other out, and no magnetism results.  Plastic pens, pieces of paper, and even people fall into this category.

• In a permanent magnet, the magnetic domains are always aligned (all pointing in the same direction).  Their magnetic fields add to one another, and the item acts as a magnet.

• Some materials have domains that are normally not lined up, but that can become lined up if a magnetic field is applied to them.  These objects (such as electromagnets, iron nails, and steel paperclips) are called temporary magnets.  They are magnets for a short time only, and only when their magnetic domains are fully aligned.

A magnetic field surrounds a moving electric charge.  Therefore, a complete circuit in which electricity is flowing also produces a magnetic field.

• The closer you get to the wire, the stronger the magnetic field.

• The more electric current flows through the wire, the stronger the magnetic field.

Magnets can also apply forces (attract and repel) to current carrying wires.  This is how electric motors are able to work.

An electromagnet is a temporary magnet turned on and off by electricity.

Electromagnets are created by taking a wire and wrapping it around a ferromagnetic core.  

Like permanent magnets, electromagnets have both a North and a South pole.

Electromagnets differ from permanent magnets in three important ways:

1. Electromagnets can be turned on and off.  Permanent magnets always have their magnetic fields on.

2. The strength of an electromagnet can be changed by adding more/taking away loops of wire around the core.  Also, you can change the strength by increasing the amount of current flowing through the wires.

3. You can reverse the poles on an electromagnet, which you can’t do on a permanent magnet.

We use electromagnets in many devices, such as loudspeakers, power tools, electric fans, hair dryers, computers, and microwave ovens.

An electric motor is a device that uses an electric current to produce motion.  It converts electrical energy into mechanical energy, using magnetism.

• A coil of wire that can turn is placed between the opposite poles of two permanent magnets.  

• Electric current begins to flow through the coil.  The magnetic field created by the electric current is attracted to the magnetic field in the permanent magnets.

• A device called a commutator reverses the direction of the current, and thus, the magnetic field created by the coil.  The like poles then repel each other and cause the coil of wire to spin.

• The commutator continues to reverse the direction of the electric current and magnetic field whenever the magnetic poles line up, keeping the motor spinning.

Magnetism can produce an electric current.  You can do this in one of two ways:

• You can move a magnet near or around a coil of wire.  As long as the magnet keeps moving in some way, you’ll create electricity in the wire.

• You can also move the coil of wire around or near a magnet.  As long as the coil of wire keeps moving, you’ll still create electricity.

You cannot create electricity in a wire by placing a magnet next to the wire and doing nothing.  Either the magnet, the coil of wire, or both must be in motion.

An electric generator is a device that uses a magnetic field to transform mechanical energy into electric energy:

• A coil of wire that can turn is placed between two permanent magnets.

• Mechanical energy turns a shaft or turbine that spins the coil of wire.

• As the coil of wire spins in between the two magnets, electricity is generated in the wire.

Most electric generators produce alternating current (the kind that comes out from an outlet on the wall).  Alternating current is electric current that changes direction in a regular pattern.

A few generators can produce direct current.  Direct current is electricity that flows in only one direction.  Batteries produce direct current.

Power plants use generators to produce large amounts of electricity.  They do this in many ways:

• Wind on a wind farm can be used to turn a fan blade, which turns a coil of wire in a magnetic field.

• Falling water behind a hydroelectric dam can be used to turn a turbine, which turns a coil of wire in a magnetic field.

• Burning coal can be used to boil water, creating a jet of steam that can also be used to turn a turbine, which turns a coil of wire in a magnetic field.