Magnetism and Electromagnets Permanent Magnet A permanent magnet

Magnetism and Electromagnets

Permanent Magnet • A permanent magnet is a material that keeps its magnetic properties, even when it is not close to other magnets.

Poles • All magnets have two opposite magnetic poles.

Attraction

Magnetic Fields • Magnetic field lines always point away from a magnet’s north pole and toward its south pole.

• What does the direction of magnetic field lines tell you? • Magnetic field lines point in the direction of the force from the north pole.

Magnetic Declination • The difference between the direction a compass points and the direction of true north.

Earth’s Magnetism • Huge electric currents flowing in the molten iron produce the Earth’s magnetic field (like an electromagnet!).

Gauss • The unit to measure the strength of a magnetic field. • Earth’s magnetic field averages about 0. 5 gauss at the surface.

Electromagnets • Magnets created by electric current flowing in wires.

Electromagnet Poles • “right-hand-rule”

Advantages • You can switch an electromagnet on and off by switching the current on and off. • You can switch an electromagnet’s north and south poles by reversing the direction of the current in the coil. • The strength can be changed by changing the amount of current in the coil. • Can be much stronger than permanent magnets when using large currents.

• http: //www. howstuffworks. com/electromagnet. htm • https: //www. youtube. com/watch? v=gz. CXowhks 80

Paramagnetic • Classified as nonmagnetic • Magnetism of individual electrons do not cancel completely. • Alignment of poles varies from atom to atom • The total magnetic field averages to zero. • Examples: ▫ Aluminum ▫ Many chemicals

Ferromagnetic • Very strong magnetic properties. • Examples: ▫ Iron ▫ Nickel ▫ Cobalt

Soft Magnet • A material that is easy to magnetize but loses its magnetization easily too. • Examples: ▫ Steel • Heat, shock, and other magnet can demagnetize steel.

Hard Magnets • Magnetism tends to remain aligned for a long time. • Demagnetized with high temperatures

Use right-hand-rule to describe the north and south pole.

• Materials in which each atom has a tiny magnetic field, but the north and south poles of atoms within the material are randomly arranged so that the magnetic fields cancel out, are known as: a. nonmagnetic. b. paramagnetic c. diamagnetic. d. monomagnetic.

• If you reverse the direction of current flow in an electromagnet: a. the north and south poles are reversed. b. the magnet is neutralized. c. the strength of the magnetic field increases. d. a short circuit occurs.

• An example of a ferromagnetic material is a: a. ceramic mug. b. nail attracted to a bar magnet. c. penny. d. CD.

• Which of the following creates a magnetic field? a. A metal ball with 2 coulombs of static charge on it b. A piece of aluminum c. A coil of wire carrying current d. A diamagnetic material