Introduction to Magnetism

Warm-up  Why does the magnet stick to the whiteboard?

History of Magnetism  The term magnetism stems from a rocks found in the region of Magnesia, Greece called lodestones.  In the 1100’s, the Chinese used magnets to help navigate their ships and created the first compasses.  In the 1700’s Charles Coulomb studied the forces between lodestones.

Hans Christian Oersted  In 1819, Danish scientist discovered the relationship between electric currents and magnetism.  This lead to a world-wide search for the links between electricity and magnetism.  We will be discussing all of these links later this week

Magnetic Poles  Why do magnets repel if they are oriented one way, but attract if they are oriented another way?

Magnetic Poles  Magnets have two poles, North and South.  The magnetic fields are strongest at the North and South poles, and weaker the farther you get away from them.

 What happens if you break a magnet? Is it possible to isolate a pole?

 Using a compass, let us find which pole is which on each magnet.  What happens when we put a North Pole near a South pole?  What happens when we put a South Pole near a North Pole?

How does a Compass Work?  If a compass is held on a table, without anything near it, how come the needle points in a specific direction?

Earth’s Magnetic Poles  The Earth has a magnetic field, so therefore, a compass with a needle that is attracted to magnetic poles (like a paper clip) points towards the poles.  Ready for the confusing part… the geographic North Pole is actually the magnetic South Pole… and it isn’t located directly North

 The magnetic South pole, is located just North of the Hudson Bay in Canada.  That is 1500km away from the Earth’s Geographic North Pole.  earth's magnetic field earth's magnetic field earth's magnetic field

Why is the Earth Magnetic?  Although the Earth has large deposits of iron ore beneath its surface (a magnetic substance), the high temperatures prevent the iron from retaining magnetism.  It is predicted that the magnetic field is due to the movement of convection currents at the Earth’s core.

Are other planets magnetic?  There is evidence that the rate of rotation is related to the strength of a planet’s magnetic field.  For example, Jupiter rotates faster than Earth and has a stronger magnetic field.

How are some rocks magnetic and some not?  Iron ore achieves magnetism because it is subjected to the Earth’s magnetic field over long periods of time.  Observe what happens to the paper clip as it is attached to a permanent magnet for a long period of time.

Magnetic Field lines  Just like electric fields, magnetic fields can be shown through field lines.  Predict what the field lines would look like for the following magnet: