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Electromagnetic Induction
A.S. 12.1.1 – 12.1.6 due Friday, 12/19/14
What happens to electrons as they move
through a magnetic field?
What would happen if there were a LOT of electrons…like in a wire…
Things to think about…
Electrons experience a force when moving
through a magnetic field If the electrons are in a wire, they all
experience a force and will move in the direction of the force
Result: A net shift in charge so that one side of the wire is more negative than the other
End result: There is an electric field created in the wire due to the separation of charges:
What happens…
The electrons (charge = e) will continue to
move to one end of the wire UNTIL… The force of electrostatic repulsion balances
the force from the magnetic field:
Induced (motional) emf
Known: An electric current produces a
magnetic field Known: A wire moving through
(perpendicular to) a magnetic field will develop a potential difference across its ends (Induced emf)
More difficult? Producing a current…
Electromagnetic Induction
What happens to the current
when: North end moved into the loop? North end moved out of the loop? South end moved into the loop? South end moved out of the loop? North end held above the plane of the loop? Magnet held inside the loop? Magnet moved in/out of the loop at a different
speed than before?
Observations
As these increase, so will the current: The relative speed of the magnet with respect to
the loop/coil Strength of the magnetic field Number of turns in the coil Area of the loop
ALSO: Angle of the magnetic field relative to the plane of
the loop. At an angle 90° (field perpendicular to the plane
of the loop), the current will be the maximum possible for the conditions
Variables that affect current:
British Physicist and Chemist—born 1791, died 1867 Self-taught…discovered many concepts, had
difficulties with some of the math Discovered Electromagnetic Induction in 1831
(also devised the laws relating to electrolysis and the deposition of ions onto metals through the use of electricity)
Found the connecting link between each of the observations we just made…
The relevant law that bears his name (Faraday’s Law) relates to electromagnetism
Michael Faraday
The strength of the magnetic field crossing
the plane of a loop of area, A
B = magnetic field strength A = area of the loop q = angle between the magnetic field
direction and the normal to the plane of the loop
Magnetic Flux
Units of flux = Weber (Wb)
Conceptual visualization: flux is the number of magnetic field lines that are passing through the plane of the loop
Increase the flux by: Increasing the area of the loop Increasing the strength of the field (more field lines…) Making the loop and field lines more perpendicular
Magnetic Flux
Same as magnetic flux…but specifically when
there is more than 1 loop in a coil.
N = number of loops in the coil
Magnetic Flux Linkage
A loop of area 2.00 cm2 is in a constant
magnetic field of 0.100 T. What is the magnetic flux through the loop in each of the following situations: When the loop is perpendicular to the field When the loop is parallel to the field When the normal to the loop and the field have
an angle of 60.0° between them?
Sample Problem
The induced emf is equal to the (negative
value for) rate of change of magnetic flux:
The induced emf, therefore, can cause a current in a conducting wire…but this will ONLY happen when there is a changing magnetic flux!
Faraday’s Law
The magnetic field through a single loop of
area 0.250 m2 is changing at a rate of 4.25 T·s-
1. What is the induced emf in the loop?
Sample Problem