Welcome Back Minions!!! Slide 2 Warm Up What are the properties
of magnets? How do magnetic poles interact? What is the shape of a
magnetic field? How can an atom behave like a magnet? How are
Magnetic Domains arranged in a magnetic material? How can magnets
be changed? How is the Earth like a bar magnet? What are the
effects of the Earths Magnetic Field? Slide 3 Whatayathink What is
electromagnetism? What are the 3 characteristics found in a
magnetic field produced by a current? What is an electromagnet?
Slide 4 Discovery! 1820 Hans Christian rsted Danish Physicist &
Chemist Experiment Current through a wire Brought a compass near
The needle moved! Slide 5 He did what? Slide 6 What is this?
Electric current produces a magnetic field. Electromagnetism
Relationship between electricity and magnetism. Slide 7 Three
Characteristics Magnetic field produced by a current has 3
characteristics 1) Field can be turned on or off. 2) Field can have
its direction reversed. 3) Field can have its strength changed.
Slide 8 Turn it On/Off Example of this is an electromagnet at a
scrap yard. Turn current on. Magnet picks up metal. Turn current
off. Magnet drops metal. Slide 9 Reversed! What do you notice about
the current? What do you notice about the field? What happens when
you switch the current? Slide 10 Stronger! When a wire is looped it
bunches up the magnetic field, increasing its strength. The more
loops, the greater the strength! Solenoid A coil of wire with a
current Slide 11 Stronger! 4 Ways Increase the current! Add more
loops of wire! Wind the coils closer together! Stronger
ferromagnetic material for the core! Slide 12 Make your own magnet!
Battery Wire Metal rod or nail Slide 13 Look familiar? Slide 14
Electromagnet What is it? Solenoid with a ferromagnetic core.
Produced by the current and the core! Overall magnetic field is
hundreds or thousands of times stronger than the field produced by
a current alone! It can be turned on and off! Slide 15
Electromagnet Remember the crane with the electromagnet? Slide 16
Right Hand Rule of Thumb The thumb points in the direction of the
magnetic NORTH POLE. The fingers curl in the direction of the
MAGNETIC FIELD. Slide 17 Lenzs Law In 1835 Heinrich Lenz stated the
law that now bears his name. An electric current induced by a
changing magnetic field will flow such that it will create its own
magnetic field that opposes the magnetic field that created it.
These opposing fields occupying the same space at the same time
result in a pair of forces. These forces are felt when you turn a
generator and generate electricity. The more current you generate,
the greater the force opposing you. Slide 18 Lenzs Law (continued)
This force can also be felt if you try to drag a conductive,
non-magnetic plate between the poles of a horseshoe magnet. The
plate sees a changing magnetic field which creates a current in the
plate, which creates its own magnetic field opposing the one that
created it. Slide 19 Lenzs Law Another great example of Lenz's law
is to take a copper tube (it's conductive but non-magnetic) and
drop a piece of metal down through the tube. The piece of steel
will fall through, as you might expect. It accelerates very close
to the acceleration due to gravity. (Only air friction and some
possible rubbing against the inside of the tube prevent it from
reaching the acceleration due to gravity.) Slide 20 Lenzs Law Now
take the same copper tube and drop a magnet through it (hopefully a
strong one, Neodymium or other rare earth magnets work the best)
You will notice that the magnet falls very slowly. This is because
the copper tube "sees" a changing magnetic field from the falling
magnet. This changing magnetic field induces a current in the
copper tube. Slide 21 Lenzs Law The induced current in the copper
tube creates its own magnetic field that opposes the magnetic field
that created it. Slide 22 Review 1)Discovered the electromagnet.
2)Discovered magnets had an electrical field. 3)Discovered currents
had a magnetic field. 4)Discovered compasses are not affected by
currents. Slide 23 Review Electromagnetism is 1) Sticky for metals.
2) Relationship between electricity and magnetism. 3) Useless in
space. 4) Relationship between magnets and wire coils. Slide 24
Review What are the 3 characteristics found in a magnetic field
produced by a current? 1) Turned on/off, repels plastic, strength
changed. 2) Turned on/off, direction reversed, series circuit. 3)
Fireproof, direction reversed, strength changed. 4) Turned on/off,
direction reversed, strength changed. Slide 25 Review What is an
electromagnet? 1) Solenoid with a ferromagnetic core. 2) Series
circuit with an iron core. 3) Parallel circuit with a reversed
current. 4) Comic book villain.
