Magnetism Magnetic materials All magnets have a North

Magnetism

Magnetic materials All magnets have a North pole and a South pole. u Just like electric charges, like poles repel and opposite poles attract. u

Remember playing with magnets as a kid?

Even breaking a magnet into smaller pieces doesn’t remove the two poles.

Magnets produce magnetic fields

How to draw magnetic field lines Magnetic field lines are always drawn outward from the North pole and inward to the South pole. u The magnetic field is strongest where the field lines are closest together. u

Similar to electric field lines!

So how do paper clips stick to a magnet?

The Earth even has a magnetic field! u In response to the Earth's magnetic field, the compass will point toward the geographic North Pole of the Earth because it is in fact a magnetic south pole. The magnetic field lines of the Earth enter the Earth near the geographic North Pole.

Applications of Magnetism u Compasses u CD and DVD files u Audio and video cassette recording u MRI scans u Aurora borealis u Homing pigeons (what? !) u Electric generators u Transformers

Some of those applications are related to electricity – why are they here? u Hans Christian Oersted discovered that an electric current produces a magnetic field. – 1 st right hand rule u Michael Faraday proved the reverse to be true; that a magnetic field produces an electric current (induction)

EMF u Electromagnetic induction is the generation of an electromotive force (EMF) in a conductor when it’s exposed to a magnetic field. u Measured in volts (J/C) so it’s the same as potential difference! u Faraday’s Law u Useful in generators and transformers

1 st right hand rule magnetic field around a current-carrying wire

1 st right hand rule magnetic field around a current-carrying wire

2 nd right hand rule direction of field around a solenoid (wire coil)

2 nd right hand rule direction of field around an electromagnet or solenoid

Relationships u The higher the current (I), the stronger the magnetic field. u The higher the number of turns (N) in the electromagnet, the stronger the magnetic field. u The voltage is proportional to the number of loops