Download Do Now (2/5/14)

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?
Intro to
Electromagnetism
Copper Tube Demo
•
You will have 10 minutes to complete the Demo Activity.
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Do not drop the magnets on the floor!
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Please ignore air resistance in your answers.
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?
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!?!
Energy Transfer
He discovered that he could induce current by
moving a wire through a magnetic field
What type of energy transfer is this?
Kinetic Energy to Electrical Energy
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
Current
•
What sort of shape do magnetic field
lines form around a current carrying
wire?
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?
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.
Lets Change Gears
What is the name of a force acting on an object
that moves in a circular path?
What is the direction of centripetal force?
Towards the center of the circle
Mass Spectrometer
•
Mass Spectrometer
o Measures the mass of an unknown atoms or molecules
RHR
•
Why does the particle curve downwards?
Radius of the Circle
Name the two forces in the diagram
Magnetic force == centripetal force
Lets solve for the radius of the circle:
mv
qB 
r
mv
r
qB
Identify our Variables
•
•
m = Mass
v = Velocity
•
•
•
r = Radius
q = Charge
B = Magnetic Field Strength
Apply RHR
Is this particle an electron or
proton?
Proton
How do we know if this particle
is an electron or proton?
RHR
Moving through a Voltage
• V = voltage
• v = velocity
• Q = Charge
• M = Mass
v
2qV
m
Classwork
Use the rest of class time to work on your
homework.
‘Interaction between E and B and matter’
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?
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
EMF
What occurs if a wire moves through a magnetic field?
A current is induced
•
•
A force is exerted on the charges in the wire.
This increases the electric potential energy on the
charges.
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.
EMF
• Electromotive Force (emf) -
IS NOT A FORCE
o 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=Blv
Where l is the length of the wire.
Classwork
Use the rest of class time to work on your
homework. Either:
‘Interaction between E and B and matter’
Or
‘Electromagnetic Induction’
Cool videos
Feel free to watch these on your own time
http://www.youtube.com/watch?v=txmKr69jGBk
magnet:
http://www.youtube.com/watch?v=FM3LVrKXFcA