Magnetic Field and Magnetic ForcesMagnetic Forces
Chapter 27October 18, 2012October 18, 2012
October 18, 2012 Physics 208 1
Announcing New SI Peer Instructor for our class
Jennifer King, [email protected] will be hosting 3 SI sessions each week for the rest of the semestersemester.
Sunday 5pm, Harrington 200Monday 8pm, Harrington 203T d 8 Bl k 105Tuesday 8pm, Blocker 105
Tuesday- discuss topics covered that day in lectureSunday- discuss topics covered in Thursday lectureMonday- review "tricky" concepts/address any lingering questions over previous week's material
October 18, 2012 Physics 208 2
Exam 2 Results
9
10
Exam 2 scores
6
7
8
ncy
A – 90-100B – 80-89C – 70-79 D – 54-69
3
4
5
Freq
uen
Frequency
D – 54-69F – 0-53
Exam Average
0
1
2
2 12 22 32 42 52 62 72 82 92 More
72
October 18, 2012 Physics 208 3
Exam 2 score
Magnetic Force on aMoving Charge
October 18, 2012 Physics 208 4
Flux of the Magnetic Field, ΦΒ
Once again we introduce theidea of Flux. This time wecalculate the flux of the magnetic field through asurfacesurface……….
October 18, 2012 Physics 208 5
Calculating flux…….
October 18, 2012 Physics 208 6
October 18, 2012 Physics 208 7
Velocity Selector
rrrrr
BvqEq
BvqEqFFF electricmagnetictotalrvr
rvrrrr
×=
×+−=+==
or
0
October 18, 2012 Physics 208 8
BvqEq ×=or
The Mass Spectrometer
October 18, 2012 Physics 208 9
Mass Spec (cont.)
EvBvqEq so×rvr
qBRmvB
vBvqEq
thenand
so =×=
RqBqBRmv
2
then and =
Eqm =
October 18, 2012 Physics 208 10
The Cyclotron
October 18, 2012 Physics 208 11
Cyclotron Frequency
revolutionahalf onefor Time
)/(
velocitydistance
21 BRmq
RvRT ππ===
radius theoft independen is this:Note so
)/(velocity
21 qB
mT
BRmqvπ
=2 qB
October 18, 2012 Physics 208 12
October 18, 2012 Physics 208 13
Force on a current carrying wire in a magnetic field…..
Remember that a wire iscarrying moving charges with a velocity of vdrift
October 18, 2012 Physics 208 14
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Example..
October 168 2012 Physics 208 16
October 168 2012 Physics 208 17
A more complicated loop to consider….
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October 18, 2012 Physics 208 19
Force on a current loop in a uniform field.
October 18, 2012 Physics 208 20
Torque on a current carrying loop
getweloopfor thesoFrrrr
×=τ
get weloopfor theso
B
Frrrr
×=
×=
μτ
τ
looptheofplanethetonormal vector a is where ANIrr
=μoopt eop a et etoo avectoas
October 18, 2012 Physics 208 21
Potential Energy of a dipole in a magnetic field
dipolemagneticthisofenergypotentialThe thenis field B uniform ain
dipolemagnetic thisofenergy potential The
BUrr
⋅−= μ
October 86, 2012 Physics 208 22
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