do now (2/5/14) do not touch the materials on your desk until instructed to do so. 1) are all metals...
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Do Now (2/5/14)Do not touch the materials on your desk until instructed to do so.
1) Are all metals magnetic?
2) Can non-magnetic materials interact with magnets?
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Intro to Electromagnetism
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Copper Tube Demo• You will have 10 minutes to complete the Demo Activity.
• Do not drop the magnets on the floor!
• Please ignore air resistance in your answers.
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Copper Tube
• What did you observe when you dropped your pencil?
• What did you observe when you dropped the magnet?
• Was the magnet attracted to the copper tube?
• What guesses did you come up with for why this occurs?
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Electric Current and Magnetism
• In 1820, it was hypothesized that the electric current must produce a magnetic field around the wire.
• Michael Faraday wondered if the reverse might be true!?!
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Energy Transfer
What type of energy transfer is this?
Kinetic Energy to Electrical Energy
He discovered that he could induce current by moving a wire through a magnetic field
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Inducing a Current
• It is the relative motion between the wire and the magnetic field that produces a current.
What if the wire moved parallel to the Magnetic Field?Would current be produced?
NO CURRENT IS PRODUCED IF THE WIRE MOVES PARALLEL TO THE MAGNETIC FIELD
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Current
• What sort of shape do magnetic field lines form around a current carrying
wire?
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Exit Question:A wire of length 10 cm moves parallel along a magnetic
field of strength 8T such that none of the field intersects the wire. If the wire is moving 500 m/min what is the resulting current through the wire?
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Do Now (2/6/14)1. What must be true for a current to be induced in a wire as the wire
moves through a magnetic field?
2. A uniform magnetic field B, with magnitude B = 1.2 x 10-3 T, points vertically upward throughout an enclosed space. A proton with a velocity v = 3.2 x 107 m/s enters the space moving horizontally from south to north.
• Find (a) the magnitude and (b) the direction of magnetic field.
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Lets Change Gears
What is the direction of centripetal force?
Towards the center of the circle
What is the name of a force acting on an object that moves in a circular path?
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Mass Spectrometer• Mass Spectrometer
o Measures the mass of an unknown atoms or molecules
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RHR• Why does the particle curve downwards?
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Radius of the CircleName the two forces in the diagram
Magnetic force == centripetal force
Lets solve for the radius of the circle:
r
mvqB
qB
mvr
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Identify our Variables
• m = Mass
• v = Velocity
• q = Charge• B = Magnetic Field Strength
• r = Radius
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Apply RHR
Is this particle an electron or proton?
Proton
RHR
How do we know if this particle is an electron or proton?
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Moving through a Voltage
• V = voltage• v = velocity• Q = Charge• M = Mass m
qVv
2
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Classwork
Use the rest of class time to work on your homework.
‘Interaction between E and B and matter’
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Do Now (2/7/14)
• An electron moves at 4.2 x 105 m/s as it passes through a magnetic field. What is the radius of it’s circular path?
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Electricity• What are different ways we generate electricity?
• Hydro-electric Dams• Wind Power• Generators• Solar Power• Fossil Fuels
What type of energy transfer is this?
Kinetic Energy to Electrical Energy
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EMF
A current is induced
• A force is exerted on the charges in the wire.
• This increases the electric potential energy on the charges.
What occurs if a wire moves through a magnetic field?
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EMF
• What have we learned before that uses the word ‘potential’?
Potential Difference! (ΔV)
This change in potential, or potential difference is called the induced electromotive force, or EMF.
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• Electromotive Force (emf) - IS NOT A FORCEo It was defined before we fully understood electricity.o Think of it as a voltage.
• The EMF (ε) is measured in volts and depends on:
ε = B l vWhere l is the length of the wire.
EMF
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Classwork
Use the rest of class time to work on your homework. Either:
‘Interaction between E and B and matter’Or
‘Electromagnetic Induction’
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Cool videosFeel free to watch these on your own time
http://www.youtube.com/watch?v=txmKr69jGBk
magnet:http://www.youtube.com/watch?v=FM3LVrKXFcA
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