Last time RC circuits. Exam 2 is Tuesday Oct. 27 5:30-7 pm, Birge 145. Magnetic force on charged particle. Magnetic force on electric charges

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Marjorie Sullivan
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1 Eam is Tuesda Oct. 7 5:0-7 pm, ige 45 Last time RC cicuits Students w / scheduled academic conflict please sta afte class TODAY to aange altenate time. Coes: all mateial since eam ook sections: Chap 7, 9, 0 (not 0.7),,.-4,.7-8 fields ing: Calculato One (double-sided) 8 / note sheet foces Eam eiew: Thusda, Oct., in class foce on electic chages Effect of unifom -field on chaged paticle Chaged paticle not moing no effect Chaged paticle is moing: Foce is pependicula to Field Paticle Velocit Depends on sign of chage foce on chaged paticle Magnitude of foce is popotional to Chage of paticle, q Speed of paticle, Stength of magnet field, sin(θ), θ=angle between and F = qsinθ Diection of foce is pependicula to both F = q and ecto coss poduct 4 F on a Chage Moing in a Field, Fomula F = q F is the magnetic foce q is the chage is the elocit of the moing chage is the magnetic field S unit of magnetic field: tesla (T) N T = C m /s = N A m CGS unit: gauss (G): T = 0 4 G (Eath suface 0.5 G) 5 Quick Qui The thee chages below hae equal chage and speed, but ae taeling in diffeent diections in a unifom Which paticle epeiences the geatest magnetic foce? A.. C. D. All same F = q sin(θ) 6

Quick Qui Foce on moing chaged paticle F = q The thee chages below hae equal chage and speed, but ae taeling in diffeent diections in a unifom The

. False 7 Field diection notation F intemediate into-page (back of aow) out-of-page (tip of aow) 8 Foce on a Cuent Field diection indicated b ecto

All foces ae into page F =0 Magnitude F = q sin(θ) A. Tue F = L foce field 0 Electic cuent poduces magnetic field Homopola moto Wh does the moto tun?

2 Quick Qui Foce on moing chaged paticle F = q The thee chages below hae equal chage and speed, but ae taeling in diffeent diections in a unifom The foce on all the paticles is in the same diection.. False 7 Field diection notation F intemediate into-page (back of aow) out-of-page (tip of aow) 8 Foce on a Cuent Field diection indicated b ecto n-plane : daw ecto Not in-plane : 9 ds Foce on staight section of wie, length L Cuent S Foce on each chage q Foce on length ds of wie N F q>0 F is ma All foces ae into page F =0 Magnitude F = q sin(θ) A. Tue F = L foce field 0 Electic cuent poduces magnetic field Homopola moto Wh does the moto tun? A. Electic Coulomb foce pushes on magnet Cuent (flow of electic chages ) in wie poduces That magnetic field aligns compass needle. field pushes on cuent fom batte Cuent C. Cuent fom batte heats the magnet D. Cuent though wie poduces magnetic field field

θ ds Law of iot-saat out of page in plane of page ds Each shot length of cuent poduces contibution to d = distance fom cuent element = 4π 0 7

to point at which field is ealuated d s ˆ Shot length of cuent Unit ecto towad point at which field is ealuated C D d s d 4 D C field fom long

on filings align with magnetic field lines field loops aound the cuent.

3 θ ds Law of iot-saat out of page in plane of page ds Each shot length of cuent poduces contibution to d = distance fom cuent element = 4π 0 7 N / A = pemeabilit of fee space d d s ˆ Field fom e shot section of cuent d s Vecto coss poduct d d s ˆ d Dist. to point at which field is ealuated d s ˆ Shot length of cuent Unit ecto towad point at which field is ealuated C D d s d 4 D C field fom long staight wie: Diection d d s ˆ field fom a cuent What diection is the magnetic field fom an infinitel-long staight wie? on filings align with magnetic field lines field loops aound the cuent. 5 6 Foces between cuents Which of these pais of cuents will attact each othe? A. A. A & C C. D. A & A C Foce between cuentcaing wies Attactie fo paallel cuents. Repulsie fo antipaallel cuents Tue. Oct. 8, 008 Phsics 08, Lectue 7 7 Tue. Oct. 8, 008 Phsics 08, Lectue 7 8

Cuent dependence How does the magnitude of the -field change if the cuent is doubled? d d s ˆ Distance dependence How does the magnitude of the -field at compae to that at?

4 Cuent dependence How does the magnitude of the -field change if the cuent is doubled? d d s ˆ Distance dependence How does the magnitude of the -field at compae to that at? d d s ˆ A) s haled ) Quaduples A) = ) = C) Stas same C) = / D) Doubles D) =4 E) s quateed E) = /4 9 0 Wh? iot-saat sas d d s ˆ Wh () / instead of /? Small contibution fom this cuent element. ~ independent of Lage contibution fom this cuent element. Deceases as / Long staight wie All cuent elements poduce out of page d ds ˆ 4π sinθ a 4π a ( + a ) / a Add them all up: a 4π θ d ( ) = / + a = + a πa Field at cente of cuent loop d s d s ˆ Contibutions fom all Contibution fom d s Diection: ˆ Magnitude: 4πR ds d s same Field fom a cicula loop Each cuent element poduce d All contibutions add as ectos Along ais, all components cancel ecept fo -comp Add them up: 4πR ds + µ o 4πR ds + µ o 4πR ds + cicumfeence = µ o ( ds 4πR + ds + ds +) = µ o 4πR πr = µ o R 4 4

5 field fom loop Which of these gaphs best epesents the magnetic field on the ais of the loop? A.. C. D. 5 5

MTE2 Wed 26, at 5:30-7:00 pm Ch2103 and SH 180. Contents of MTE2. Study chapters (no 32.6, 32.10, no 32.8 forces between wires)

MTE2 Wed 26, at 5:30-7:00 pm Ch2103 and SH 180. Contents of MTE2. Study chapters (no 32.6, 32.10, no 32.8 forces between wires) MTE Wed 6, at 5:30-7:00 pm Ch03 and SH 80 Contents of MTE Wok of the electic foce and potential enegy Electic Potential and ield Capacitos and capacitance Cuent and esistance, Ohm s la DC Cicuits and Kichoff