New Magnetic Field and Magnetic ForcesMagnetic...

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, jenn4k08_2012@neo.tamu.eduShe 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

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 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