Magnetism Ch. 12

How does Magnetism Compare to Electrical Charges? Like Charges repel, unlike charges attract Like Poles will repel, unlike poles attract These forces allow both magnetic poles and electric charges to “line up” with opposite forces—kind of like a force pair

How are they different? Magnetic Poles always come in pairs (like heads and tails on a coin) Electric charges can come in pairs but they can also be separated (protons in the nucleus, electrons outside)

Magnetic Field These are regions of magnetic influence Areas where objects are pulled by a magnetic force Surround an electric field—cannot have one without the other.

What causes Magnetism? It is caused by constant electron motion Electron move in 2 ways (just like the Earth) They spin on their axis (like a top) They revolve around the nucleus

Current Carrying Wire Do wires that carry current have a magnetic field?

You can’t have one without the other By definition, one moving charge makes a magnetic field Therefore, a whole current of electric charges will make a larger magnetic field This magnetic field goes in circles around the wire (see p. 196) If the current changes direction the circles will also change directions

Why are some metals metallic and some not? Depends on magnetic domains (p. 195) If the atoms are aligned they are magnetic If they are not aligned they are not magnetic If a magnet is dropped on a hard floor, what will happen?

Electromagnetic Induction Anytime you change a magnetic force, (distance or strength), you induce an electromagnetic field -Move a magnet closer or further away from an electric current -Or if you change the amount of electric current, an EM field is produced

What is this? Why?

Earth is a giant magnet One end of every magnet will spin to the north if possible. This has been used for over 2,000 years to help guide travelers. A compass is a freely spinning magnet.

William Gilbert Responsible for fine-tuning the idea of a compass in the early 1600s First to suggest that Earth was a magnet. Said the Earth has a giant bar magnet running through its center, and the magnetic poles were near the geographic poles

North or South Pole A compass always points which direction? Doesn’t that mean it should be attracting to it’s opposite pole? So what is actually near the geographic North Pole?

How a compass works A compass needle points north because it is strongly attracted to a magnetic south pole The magnetic poles are not straight up and down, but rather they are tilted See Diagram on Board