Magnetism

Physical Science

What is a magnet?

2000 years ago the Greeks discovered a mineral that attracted things made of iron.

They named this mineral Magnetite because it was discovered in Turkey near the town call Magnesia.

Magnet is any material that attracts iron or things made from iron.

Magnetism

Ferromagnets ~naturally occurring magnets Fe, Co, Ni

Magnetic forces are similar to electrical forces

Magnetic Poles Magnets have 2 poles

(dipole) – North & South

Can never be a monopole

Rule: Like poles repel; opposite poles attract

Magnetic Poles

If you broke a magnet in half, you would have 2 magnets!

Magnetic Fields

Magnetic Field space around a magnet Produced by

moving electric charges (electrons in motion)

Domains - clusters of aligned atoms in a substance

Magnetic Fields

We have a magnetic field on Earth!

Magnetic Fields

A little more on domains….

Electric Currents and Magnetic Fields When an electric current passes

through a wire a magnetic field is formed

Electric Currents and Magnetic Fields

When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an Electromagnet It’s strength is increased by increasing

the current through the coil.

Electric Currents and Magnetic Fields

Electromagnets:

Magnetic Forces are Exerted on Moving Charges

A charged particle has to be moving to interact with a magnetic field.

Moving charges are deflected only when they cross through a magnetic field

Magnetic Force on Current-Carrying Wire Current of charges forces can also

experience deflecting force

Magnetic Forces are Exerted on Moving Charges

Electric Meters Galvanometer May be calibrated to measure current or

voltage

Electric Motors – any device that converts electric energy into kinetic energy

The magnetic field around a current-carrying wire will cause it to be pushed or pulled by a magnet converting electric energy into kinetic energy.

The current carrying wire is in a loop causing it to spin.

Earth’s Magnetosphere

Earth’s magnetic field pushes and pulls on the electric current produced by the sun.

Most of the charged particles from the sun are deflected protecting living things on Earth Aurora (Northern Lights) are due to the

charges from the Sun

Electromagnetic Induction – Using Magnets to create current

Electric current can be produced from magnetism

Motion of magnet in coil of wire Induced voltage affected by

Number of loops of wire Magnitude of motion (fast vs. slow)

Electromagnetic Induction – How Voltage is Created

Faraday’s Law summarizes electromagnetic induction Changing an electric field causes a

magnetic field Links electricity to magnetism

An electric field is induced in any region of space in which a magnetic field is changing with time

1832 British physicist Michael Faraday

Electromagnetic Induction – How Voltage is Created

Faraday’s Law states: The induced voltage in a coil is

proportional to the number of loops multiplied by the rate at which the magnetic field changes within the loops.

Power Production

Generators don’t produce energy – they convert energy from some other form to electrical energy

Nikola Tesla And George Westinghouse used Faradays findings and put them to use.

They showed electricity could be generated!

Generators and Alternating Current

A generator is just a motor in reverse Generator = mechanical energy in,

electrical energy out Motor = electrical energy in,

mechanical energy out

Generators and Alternating Current A simple generator.

Voltage is induced in the loop when it is rotated through the magnetic field

A power source spins the wire loop and with each half turn the current in the loop changes direction. (+ to -) Alternating Current

(AC) is what we use in our homes

Direct Current

A battery produces direct current (DC)

Electrons flow in one direction

Power Plants Electric generators produce almost all of the

electric energy used in the world. Gas, coal, and water are used to provide the kinetic

energy to rotate the magnetic coils

Electric energy is carried from power plants to your home through wires at high voltage which is not safe for home use Transformers – changes the voltage of AC without

losing much energy to heat The # of coils on each side of the transformer

determines the ratio of change

Superconductors

Have no resistance to the flow of electrons

Repel magnets Used to accelerate subatomic

particles to nearly the speed of light

MRI

Magnetic Resonance Imaging uses magnetic fields to create images inside of a human body without tissue damage

Strong magnetic field inside the MRI uses natural magnetism of hydrogen atoms to make a picture