Download 08 electromagnetic induction

Electromagnetic Induction
Electromagnetic Induction refers to the generation of a magnetic field from the movement of an electron.
Hans Oersted, in 1819 ­1820 discovered that moving charges (electron not yet discovered) create a magnetic field perpendicular to the moving charge
No Current
side view
With Current
Implications
A dipole or domain is created when __________________________________
The domains of a material are "saturated" when ________________________
_______________________________________________________________
The magnetic field strength can be calculated at distance r from the wire through the following equation. B = μI
2 πr
­7 .
μ = 4π x 10 T m/A for air
and B is measured in Tesla (T)
Technology benefited greatly when this knowledge was manipulated by looping the wire ("current carrying conductor")
The magnetic field was further increased by
Magnetic Field strength for Coils
1._________________________
2._________________________
B = μNI
2r
flat coil
B = μNI
L
long coil
3._________________________
4._________________________
A flat coil has r ≫ L
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Right Rule and Left Hand Rules
The following excerpt is from the University of Oregon
http://web.engr.oregonstate.edu/~traylor/ece112/lectures/elect_flow_vs_conv_I.pdf
Electron Current vs. Conventional Current
In 1752, prior to electricity being identified with the electron, Ben Franklin chose a convention
regarding the direction of current flow. Franklin assumed that electrons (being assumed positive)
flow from positive to negative terminals. We now know this is incorrect. The charge on an electron
is negative by definition (note negative sign): (­1.6x10­19 C)
The flow of electrons is termed electron current. Electrons flow from the negative terminal to the
positive. Conventional current or simply current, behaves as if positive charge carriers cause current
flow. Conventional current flows from the positive terminal to the negative.
Perhaps the clearest way to think about this is to pretend as if movement of positive charge carriers
constituted current flow.
It is important to realize that the difference between conventional current flow and electron flow in
no way effects any real­world behavior or computational results. In general, analyzing an electrical
circuit yields results that are independent of the assumed direction of current flow. Conventional
current flow is the standard that most all of the world follows.
We will use the electron flow convention in grade 11 and the conventional current flow in grade 12.
When determining the direction of any fields,
Electron Flow Convention requires the use of the __________ hand.
Conventional Current flow requires the use of the __________ hand.
The curriculum requires that students know there are two conventions!
The Motor Principle
by definition
A current­carrying conductor in an external magnetic field experiences a force directed at right angles to the plane formed by the current and the field .
by logic
• two magnets will exert a force on one another
• one maget will exert a force on a wire if it is carrying a current (or on an electron moving)
• two moving charges create magnetic fields which will result in a force!
Students have to be prepared to analyze all 3
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More on The Motor Principle
Moving charges make ______________________________________
(Oersted)
Opposite poles ____________ and like poles ______________
Looping a wire allows the magnetic field to be _____________
Factors which affect the strength of the magnetic field are
2. ___________________
1. ___________________
4. ___________________
3. ___________________
Motor Principle is a result of Oersted ­ determine the direction of force for each case.
1.
3.
S
N
S
N
5.
S
N
2.
S
N
N
S
4.
6.
A new ________ rule was developed for cases 5 and 6 ­ the force is out of your palm
AND Moving or changing magnetic fields create a _______________
(Faraday)
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The simple electric motor is a technological manipulation of the motor principle. By using a coil, the induced magnetic field is strong enough to "do work" on other things.
http://www.sasked.gov.sk.ca/docs/physics/u7c3phy.html
shows an animation of a motor
The previous page drawings are stills of what is happening continually in the flash.
New ­ Lenz's Law
Lenz used the law of energy conservation to argue the direction of the induced current as put forth by Faraday ­ the current that is induced when a magnetic field is changed or moved.
S
N
S
N
How a motor becomes a generator ­ it is _______________________ ________
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A looped wire can be called one of 3 things
• an _______________________ or a _____________ or a __________________
Michael Faraday discovered the inverse property between magnets and current electricity. Faraday discoved that one can induce a current (__________ a current) whenever one moves or changes a magnetic field near a current carrying conductor (___________)
A turbine manipulates this property to generate electricity. Most electricity production is done through mechanically turning a turbine ­ a magnet near a current carrying wire to produce electricity. To make the process more efficient, the wire is
.
1._________________________
2._________________________
3._________________________
4._________________________
Also, to improve efficiency, the device is _____________.
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