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Magnetic field is established byPermanent magnetElectric current in a magnetMoving charge
There is NO MAGNETIC MONOPOLEA moving charge (current) creates a magneticfield in the surrounding spaceThe magnetic field exerts a force on any other
moving charge /current that is present in the field
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MAGNETIC FORCE= proportional tothe charge, velocity and magnetic
field.
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SOME NOTES ON MAGNETIC FIELD LINES
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F B = q( v x B )
MAGNETIC FORCE ON A MOVING CHARGED PARTICLE
When theparticle is
at rest,the
magneticforce is
equal toZERO
When the velocityand the magnetic
field are parallel/antiparallel to eachother (perpendicularcomponent is zero),
FB is zero.
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Magnetic Flux,B = surface B cos dA
= surfaceB
dA
= surface B d A= B A= [Tesla meter 2
, T m 2 ]= [ Weber, Wb]
MAGNETIC FLUX
Unitflux=1Wb=1T(m 2)=
1Nm/A
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Magnetic Field/Magnetic Flux density=flux per unit area across an area at right angles to the
magnetic field
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2
11
1
22
2102112
1
212
2
121
i N
i N M
l
A N N M M M
dt
di
M dt
di
M
MUTUAL INDUCTANCE
EQUAL M, differentchanges in current
Negative signs are a reflection of lenzs law.
These saythat a
change incurrent in coil
1 causes achange in
flux in coil 2,inducing anemf in thecoil 2 that
opposes theflux change.
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SI unit of inductance is called theHenry=1 weber per ampere
=one volt second per ampere=one ohm-second=1 joule per ampere squared
Examples:A. If a tesla coil has a long solenoid with length l and cross sectional area A is
closely wound with N1 turns of wire, and another coil with N2 turns surroundsit at its center, find the mutual inductance.
= N1N2A l
B.
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SELF INDUCTANCE-in a circuit, when there is current, there is a magnetic field,that causes a magnetic flux, that changes when currentchanges :D THEREFORE any circuit that carries a varyingcurrent will have an emf induced by the variation in its ownmagnetic field.
l
A N L
i
N L
dt
di L
SOLENOID
2
0
1
Notice that whenwe transposedi/dt, the self
inductance is justequal to the emf
per unit rate ofchange of
current.
Inductors=purpose is to oppose any variations in the current throughthe circuit
Depends on geometry: size,shape and N
Proportional to Nsquared
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Between the terminals of an inductor, the potential difference is
equal to : V ab = Va Vb = L (di/dt)
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MAGNETIC FIELD ENERGY
2
2
LI U M
Stored energy in an inductor
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