Magnetism

Chapters 36 & 37

General Info.

Moving charges cause magnetism Magnets have magnetic fields around them.

(Magnetism acts at a distance. ) Magnets always have two, opposite poles

(“north” and “south”). Like poles repel and unlike poles attract. Compasses are magnets Spinning electrons are magnets

Can any material be magnetized?

Non-magnetic material

Magnetic material

No…only materials which have aligned unpaired, electrons can be magnetized!

Ferromagnets (“Permanent Magnets)

Fe, Ni, and Co have unpaired electrons are aligned in areas called “domains”.

Each domain has a magnetic field. When domains are aligned, material has an

overall magnetic field. Pieces of Fe, Ni, and Co become magnetized

when they are placed in a strong magnetic field which aligns their domains .

Magnetic Domains

Unaligned

Aligned

Electromagnets

DEF: magnet with a field produced by electric current

Usually a coil of wire with current and Fe core

How could you make an electromagnet stronger?

Add coils Increase current Increase amount of Fe inside

This electromagnet uses 210 lb of Fe for the core!

Force Fields

Every ________ is surrounded by a gravitational field because it attracts every other _________.

Every ________ is surrounded by an electric field because it attracts or repels every other ________.

Every _______ is surrounded by a magnetic field because it attracts/repels every other ____________.

Test Your Knowledge

Particle Grav Field? Elec Field? Mag Field?

Stationary neutron

Moving neutron

Stationary proton

Moving proton

Stationary electron

Moving electron

Magnetic Fields

DEF: the area around a magnet where a force acts on a moving charge (another magnet, a current-carrying wire, an electron, etc…)

Represented by field lines which show direction and strength of force; lines point from north to south; closer lines mean stronger field

Bar Magnet

Earth’s magnetic field looks like that of a bar magnet!

South Magnetic Pole

North Magnetic Pole

Earth’s Field

Thought to be caused by moving charges in Earth’s outer core (which is liquid).

Protects life on Earth from harmful radiation (moving charges from space).

Changes strength and direction over time. Sometimes disappears altogether!

What did you learn today?

1. List two types of metals that can be magnetized.

2. Sketch the magnetic field lines for a bar magnet.

3. Sketch the magnetic field lines of Earth.

4. In what ways is Earth’s magnetic field important to life as we know it?

Right hand rule #1

Field around a current-carrying wire—thumb in direction of current, fingers curl in direction of field

Right hand rule #2

Field inside a coil of wire—fingers in direction of current, thumb points in direction of field

Right hand rule 3

Force on a current-carrying wire/moving charge in a magnetic field—Make an “L”…fingers in direction of magnetic field, thumb in direction of current, palm points in direction of force on charge

How would the direction of the force differ on a positive charge? A negative charge?

Right Hand Rules

1. Field around a current-carrying wire—thumb in direction of current, fingers curl in direction of field

2. Field inside a coil of wire—fingers in direction of current, thumb points in direction of field

3. Force on a moving charge in a magnetic field—Make an “L”…fingers in direction of magnetic field, thumb in direction of moving charge, palm points in direction of force on charge

Right Hand Rule Applet

http://www.walter-fendt.de/ph14e/