Electromagnetism

Physics 100

Chapt 15

Michael Faraday

General circuit

+ -

Appliance+ -

Energy source(device that separates+ & - charge)

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I

Moving a Conductor in a B-fieldseparates + & - charges

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Use this to drive an electric circuit

+

+I

+

+

+

Moving wire loop in a B field

+

+

v

An electric current is“induced” in the loop

Either the magnet or the loop can move

+

+

v

an electric current is“induced” in the loop

Magnetic flux () thru a loop

= BA┴

Flux thru a coil of N loops

= N BA┴

Faraday’s law

change in N BA┴

elapsed time

Induced voltage in a circuit =change in elapsed time

EMF =

“Electro-Motive Force”

Michael Faraday

Rotating coil in B field

A┴ = 0 =0

B

Rotating coil in B field

A┴ = Acoil = maximum

B

Rotating coil in B field

A┴ = 0 (again) = 0

B

AC voltage

Lenz’ Law

v v

B B

+ +

N

S

the fall producesan induced current

the B-field producedby the induced currenttries to impede the fall

B-field from induced current

B-field from induced current

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Lenz’ law

An induced voltage always gives rise to an electric current that creates a magnetic field that opposes the influence that produced it.

Maglev trains

Maglev