Faradays Law and Induction - Lenz's Law
FB (pronounced phi) is defined as the magnetic flux for a uniform magnetic field
FB = BperpA = BAcosq where Bperp is the component of B perpendicular to the loop of area A and q is the angle between B and a line perpendicular to the loop
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| q = 90 degrees, flux is minimum (cos q = 0) | q = 0 degrees, flux is maximum (cos q = 1) |
Faraday's Law of Induction, one of the basic laws of electromagnetism
x = induced emf x is pronounced ksai
x =
- DFB/Dt This is Faraday's law of Induction
If there are N loops of wire, then they add and we arrive at
x = - NDFB/Dt
These approaches derive from the Faraday's law above
(1) Changing the magnetic field, B
(2) Changing the area of the coil, A
(3) Changing the loop's orientation, q, with respect to the field q is pronounced theta
A current produced by an induced emf moves in a direction so that its magnetic field opposes the original change in flux
Faraday's Law: http://www.youtube.com/watch?v=stUDqGzpev8
Lenz's Law:
http://www.youtube.com/watch?v=sPLawCXvKmg
Two bar magnets of the same size are dropped through
an aluminum tube and a glass tube. The magnet dropped in the glass tube
falls at the normal rate of acceleration due to gravity, but the magnet
falling through the metal tube is slowed.
This slowed acceleration occurs because the falling magnet induces currents
inside the metal tube. The induced currents then produce a small magnetic
field that opposes the direction of the original magnetic field. This effect
is known as Lenz's Law, a result of Faraday's law of induction