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• Magnetic Field and Magnetic ForcesMagnetic Forces

Chapter 27 October 18, 2012October 18, 2012

October 18, 2012 Physics 208 1

• Announcing New SI Peer Instructor for our class

Jennifer King, jenn4k08_2012@neo.tamu.edu She will be hosting 3 SI sessions each week for the rest of the semestersemester.

Sunday 5pm, Harrington 200 Monday 8pm, Harrington 203 T d 8 Bl k 105Tuesday 8pm, Blocker 105

Tuesday- discuss topics covered that day in lecture Sunday- discuss topics covered in Thursday lecture Monday- 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

n cy

A – 90-100 B – 80-89 C – 70-79 D – 54-69

3

4

5

Fr eq

u en

Frequency

D – 54-69 F – 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 a Moving Charge

October 18, 2012 Physics 208 4

• Flux of the Magnetic Field, ΦΒ

Once again we introduce the idea of Flux. This time we calculate the flux of the magnetic field through a surfacesurface……….

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 electricmagnetictotal rvr

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

qBRmv B

vBvqEq

thenand

so =×=

RqB qBRmv

2

then and =

E qm =

October 18, 2012 Physics 208 10

• The Cyclotron

October 18, 2012 Physics 208 11

• Cyclotron Frequency

revolutionahalf onefor Time

)/(

velocity distance

2 1 BRmq

R v RT ππ ===

radius theoft independen is this:Note so

)/(velocity

2 1 qB

mT

BRmqv π

= 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 is carrying moving charges with a velocity of vdrift

October 18, 2012 Physics 208 14

• October 18, 2012 Physics 208 15

• Example..

October 168 2012 Physics 208 16

• October 168 2012 Physics 208 17

• A more complicated loop to consider….

October 18, 2012 Physics 208 18

• 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 thesoFr rrr

×=τ

get weloopfor theso

B

Fr rrr

×=

×=

μτ

τ

looptheofplanethetonormal vector a is where ANI rr

=μ oopt 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

BU rr

⋅−= μ

October 86, 2012 Physics 208 22

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