►How long has the existence of How long has the existence of magnets and magnetic fields been magnets and magnetic fields been known?known?

►The existence of magnets and The existence of magnets and magnetic fields has been known for magnetic fields has been known for more than 2000 years. 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?Where was the word “magnetic” derived from?

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

►How was the first compass made? Who How was the first compass made? Who made it? made it?

►The Chinese discovered that a lodestone, The Chinese discovered that a lodestone, when floated on a cork board in a dish of when floated on a cork board in a dish of water would align itself to face north.water would align itself to face north.

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

Like poles Like poles REPELREPEL. Unlike poles . Unlike poles ATTRACTATTRACT..

Could you separate the poles of a bar Could you separate the poles of a bar magnet by breaking it in half? Why?magnet by breaking it in half? Why?

►No, if you break a magnet in half, you No, if you break a magnet in half, you create two smaller magnets, but each create two smaller magnets, but each still has two poles. still has two poles.

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

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

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

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

Bar Magnet

____ → ____

Draw the appropriate magnetic field lines for the following Draw the appropriate magnetic field lines for the following examples.examples.

►Magnetic flux (Magnetic flux (BB) – ) – a vector quantity a vector quantity representing the number of magnetic representing the number of magnetic field lines that pass through a given field lines that pass through a given area.area. The magnetic field is strongest where The magnetic field is strongest where

the lines are closest together. (most the lines are closest together. (most concentrated at poles)concentrated at poles)►Unit -Unit - Tesla (T) = kg / sTesla (T) = kg / s22••AA

In Across Out

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

How does electric charge affect a How does electric charge affect a magnet?magnet?

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

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

1.1. Magnetically charged bodies always have Magnetically charged bodies always have two two polespoles; electrically charged objects ; electrically charged objects do notdo not..

2.2. Magnetic charges last for Magnetic charges last for many yearsmany years; ; magnets magnets do notdo not have to be charged each have to be charged each time you use them. Electric charges diminish time you use them. Electric charges diminish in a few minutes, although they may last in a few minutes, although they may last several daysseveral days..

3.3. A A ““snapsnap”” is sometimes heard when electrical is sometimes heard when electrical objects are charged up or discharged. objects are charged up or discharged. No No such snapsuch snap is heard for magnetic charging. is heard for magnetic charging.

4.4. All materialsAll materials respond strongly to electrical respond strongly to electrical charge; only charge; only a few materialsa few materials are strongly are strongly magnetic.magnetic.

Stationary Charged Particle Moving Charged Particle

Magnetic Fields and Charged Magnetic Fields and Charged ParticlesParticles

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

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

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

Why is there a force on a moving Why is there a force on a moving charged particle in a magnetic field?charged particle in a magnetic field?

► Moving charges create their own magnetic Moving charges create their own magnetic field which repel from the field that it is field which repel from the field that it is traveling through.traveling through.

► A stationary charge located in the magnetic A stationary charge located in the magnetic region would experience NO force. region would experience NO force.

In order for a charge to experience a In order for a charge to experience a force exerted by a magnetic field, it force exerted by a magnetic field, it must:must:

1.1. be moving (no magnetic force acts on be moving (no magnetic force acts on a stationary charge).a stationary charge).

2.2. moving perpendicular to the direction moving perpendicular to the direction of the magnetic field (attempting to of the magnetic field (attempting to cross field lines).cross field lines).

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

Compare the motion of a charged Compare the motion of a charged particle in an electric field with its particle in an electric field with its

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

► Faraday found that to Faraday found that to generate current either…generate current either…

The conductor can move The conductor can move through a magnetic field.through a magnetic field.

OROR

The magnetic field can The magnetic field can move past a conductor.move past a conductor.

►Electromotive Force (Electromotive Force (EMFEMF) – ) – the the potential difference that is produced potential difference that is produced by electromagnetic inductionby electromagnetic induction More voltage is created by moving quickly More voltage is created by moving quickly

and perpendicular to the magnetic fieldand perpendicular to the magnetic field

Units –Units – Volts (V)Volts (V)

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

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