magnets electromagnets probe
TRANSCRIPT
Radio conversation between two ships passing in the night...
Voice 1: "We can see your lights and you are on a collision course with our vessel. Please divert your course 15 degrees to the North to avoid a collision."Voice 2: "I can see your lights too and recommend you divert your course 15 degrees to the South to avoid a collision."Voice 1: "This is the captain of a US Navy ship. I say again, divert YOUR course."Voice 2: "No, I say again, you divert YOUR course."Voice 1: "I am in the U.S.S. Wolverine, the largest battleship on this ocean. I DEMAND that you change your course one-five degrees North!"Voice 2: "I am in the Point Amour lighthouse. Your call, sir."
Magnetism MagnetismI. Characteristics of Magnets
(p.624-627) Magnetism Magnetic poles Magnetic field Magnetic domain
What are magnets?Magnets are metal objects that create
magnetic fields and attract other objects containing iron, nickel or cobalt.
Properties of Magnets
Attract iron, nickel and cobaltHave magnetic polesExert magnetic forcesSurrounded by a magnetic field
what else do we know that is surrounded by a field??
A. MagnetismMagnetism
force of attraction or repulsion between unlike or like poles
due to the arrangement of electrons
closely related to electricity
The SI unit is tesla (T)
Magnetic Poles
The strongest force on a magnet is found at the ends of the magnet
The ends of the magnet are called the Poles If you tie a string to a magnet, the part that is
the “north” always points to the north pole of the Earth.
There are North and South poles on ALL magnets.
B. Magnetic PolesMagnetic Poles
like poles repel
unlike poles attract
a broken magnet creates new poles
Magnetic ForcesThis is the push or pull a magnet causes. If two poles are the same they _______
If two poles are opposite they _______ What have we talked about that also has
forces that work this way?
Magnetic FieldThe region around a magnet in which
magnetic forces can act or are effective.The magnetic field is strongest around the
poles!
C. Magnetic FieldMagnetic Field
area around a magnet where magnetic forces act
field lines show direction of field (NS)
D. Magnetic DomainMagnetic Domain
groups of atoms with aligned magnetic poles
in a magnetized object, domains are all aligned
domain
All materials are not magnetic The atoms in matter cause magnetism
All atoms have a north and south pole created by the movement of electrons.
In most substances the atoms are arranged such that the magnetic fields are canceled.
In other matter, like iron, nickel and cobalt, the atoms group together in regions called domains. These domains can become aligned. If most of the domains are aligned, the object becomes magnetic.
Objects containing iron, nickel or cobalt can be magnetized by aligning the domains.Magnets can lose magnetic properties if these atoms lose alignment
By striking or dropping a magnet too hard By heating a magnet to high temperatures
You cannot have half a magnet.
Types of Magnets Ferromagnets
Natural magnets made of iron, cobalt or nickel
Electromagnets Usually with an iron core and made by an electric current
Permanent Difficult to magnetize but retain properties
Temporary Easy to magnetize but lose properties easily
Earth as a MagnetThe Earth acts as if it has a bar magnet
running through it!The geographic North Pole is the magnetic
South Pole.The Earth’s geographic
poles are on the axis
around which Earth spins.The spinning of Earth’s
iron and nickel core causes alignment of electrons, thus the magnetic field.
AuroraThe Aurora Borialis and Aurora Australis are
“light shows” that are caused by charged particles from the sun interacting with our upper atmosphere. These are usually visible in the far north and south because this is where the magnetic field is dipping back into the earth.
Recap!!1) What are 4 magnetic properties?2) How do magnetic forces interact?3) Why are some materials magnets while
others are not?
Magnetism MagnetismIII. Producing Electric Current
(p.633-639) Electromagnetic Induction Electric Generator DC & AC Transformer
Introduction to Magnetism from Electricity
Ever heard of Maglev??
Discovery of Electromagnetism
Discovered by a man named Hans Oersted.
His research concluded that an electric current produces a magnetic field in the direction of a given current
Electromagnetism is the interaction between electricity and magnetism.
A. Electromagnetic InductionElectromagnetic Induction
producing a current by moving a wire through a magnetic field
some microphones work just like mini-speakers in reverse
sound waves cause coil to move current
Dynamic Microphone
Coil
B. Electric GeneratorElectric Generator
mechanical energy electrical energy
armature is rotated between magnet poles
magnetic field induces a current in the wire coil
MOTORGENERATOR
B. Electric Generator Hydroelectric Dam
PE of lake water is converted to KE
mechanical KE turns the generator shaft which creates electrical energy
C. DC & ACDirect Current (DC)
current flows in one direction dry cells
Alternating Current (AC) current reverses its direction
at regular intervals electrical outlets
D. TransformerTransformer
increases or decreases AC voltage primary coil AC produces a magnetic field that
induces AC in the secondary coil voltage ratio = ratio of turns in each coil
D. TransformerStep-up Transformer
increases the voltage more turns power plants
Step-down Transformer decreases the voltage fewer turns household appliances
(hairdryers, etc.)
Magnetism MagnetismII. Uses of Magnetic Fields
(p.628-632) Electromagnet Speaker Motor
ElectromagnetElectromagnet
strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core
acts like a bar magnet when current is on
SpeakerSpeaker
electrical energy mechanical energy
wire coil moves back & forth as its magnetic field interacts with the field of a fixed magnet
forced vibration causes the cone to move sound
Video
MotorMotor
electrical energy mechanical energy
electromagnet rotates between the poles of a fixed magnet
commutator reverses the poles of the e’magnet
Motor
brushes & wires to battery field magnet
armature & commutatorassembled motor