► How long has the existence of magnets and magnetic fields been known? ► The existence of magnets and magnetic fields has been known for more than 2000 years. Legends told of lodestone hills along the Indian coast so powerful that no ship held together by iron nails dared sail past. This picture shows the resulting tragedy as the nails fly to the hills and the passengers sink into the water.

► Where was the word “magnetic” derived from? ► “Magnetic” is derived from the word Magnesia; the place where such rocks were first found.

► How was the first compass made? Who made it? ► The Chinese discovered that a lodestone, when floated on a cork board in a dish of water would align itself to face north.

► Lodestone (Magnetite) – a naturally occurring magnetic iron ore.

Like poles REPEL. Unlike poles ATTRACT.

Could you separate the poles of a bar magnet by breaking it in half? Why? ► No, if you break a magnet in half, you create two smaller magnets, but each still has two poles.

► Permanent (Hard) magnet - a material that retains its magnetic properties after an external magnetic field is removed.

► Temporary (Soft) magnet - A material that shows magnetic properties only while exposed to an external magnetic field.

► Electromagnet - A coil of wire wound about a magnetic material, such as iron, that produces a magnetic field when current flows through the wire.

► Polarization - the temporary alignment of the magnetic domains in a magnetic material when it is placed near a magnet.

Bar Magnet

____ → ____

Draw the appropriate magnetic field lines for the following examples.

► Magnetic flux (B) – a vector quantity representing the number of magnetic field lines that pass through a given area.  The magnetic field is strongest where the lines are closest together. (most concentrated at poles) ► Unit - Tesla (T) = kg / s 2 A

In Across Out

Which picture has a greater magnetic field intensity (magnetic flux)?

How does electric charge affect a magnet? ► In 1820, Danish physicist Hans Christian Oersted discovered that when a wire carrying an electric current is brought near a magnet the compass needle is deflected perpendicular to the wire.

► Electromagnetism works on the principle that an electric current through a wire generates a magnetic field.

1. Magnetically charged bodies always have two poles; electrically charged objects do not. 2. Magnetic charges last for many years; magnets do not have to be charged each time you use them. Electric charges diminish in a few minutes, although they may last several days. 3. A “snap” is sometimes heard when electrical objects are charged up or discharged. No such snap is heard for magnetic charging. 4. All materials respond strongly to electrical charge; only a few materials are strongly magnetic.

Stationary Charged ParticleMoving Charged Particle Magnetic Fields and Charged Particles

Does the Earth’s magnetic north pole lay at the geographic north pole? No, the Earth’s magnetic north pole is located near the Earth’s geographic south pole.

The earth’s magnetic field is caused by convection currents of the molten iron in the earth’s core. These convection currents cause the charged ions and electrons to move, thus producing a magnetic field.

► Streams of electrically charged particles (solar wind) are deflected by the Earth’s magnetic field into the poles.

► They collide with atoms in the Earth’s atmosphere and make them release energy in the form of flashes of light.

Why is there a force on a moving charged particle in a magnetic field? ► Moving charges create their own magnetic field which repel from the field that it is traveling through. ► A stationary charge located in the magnetic region would experience NO force.

In order for a charge to experience a force exerted by a magnetic field, it must: 1. be moving (no magnetic force acts on a stationary charge). 2. moving perpendicular to the direction of the magnetic field (attempting to cross field lines).

In which of the following pictures will the charge experience a force? Explain.

Compare the motion of a charged particle in an electric field with its motion in a magnetic field. The motion of a charged particle in an electric field is parallel to the field, meanwhile a charge in a magnetic field moves perpendicular to the field.

► Electromagnetic Induction – the generation of current through a circuit due to relative motion between a wire and a magnetic field.

► Faraday found that to generate current either…  The conductor can move through a magnetic field. OR  The magnetic field can move past a conductor.

► Electromotive Force (EMF) – the potential difference that is produced by electromagnetic induction  More voltage is created by moving quickly and perpendicular to the magnetic field  Units – Volts (V)

Motor – current provided by a power source, magnetic field causes force on current

► Generator – coil is rotated by engine, magnetic field forces a current