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