Physics Spring 2012 Announcements: Mar 07, 2012

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1 Physics 00 - Sping 01 Announcements: Ma 07, 01 HW#6 due date has been extended to the moning of Wed. Ma 1. Test # (i. Ma ) will cove only chaptes 0 and 1 All of chapte will be coveed in Test #4!!! Test # will cove all of HW#5, and though HW#6, poblem 11. Thee will be anothe in-class test eview session in pepaation fo Test # on Wed. Ma 1. 1

2 1.5 The oce on a Cuent in a Magnetic ield Example: A wie caies a cuent of.0 A fom west to east. Assume that at this location the magnetic field of Eath is hoizontal and diected fom south to noth and that it has a magnitude of = T. (a) ind the magnitude and diection of the magnetic foce on a 6.0 m length of wie. (b) Calculate the gavitational foce on the same length of wie if it s made of coppe and has a coss-sectional aea of m. Solution : (a) y RHR-1 thefoce is pointing upwad whee is the angle between the diection of the cuent segment and Hee (b) Density of coppe is Massof M G G ILsin ( / 90 wie : 199 kg/m )( Mg ( kg)(9.81 m/s IL (.0 A)(6.0 m)( M ( volume) AL ) 6 m kg/m )(6.0 m) 7.89 N -5 T) kg the magnetic N (up) field

1.6 The Toque on a Cuent-Caying Coil 1 w sin The toque is maximum when the nomal of the loop is pependicula to the magnetic field, and zeo when the nomal is paallel to the field.

3 1.6 The Toque on a Cuent-Caying Coil 1 w sin The toque is maximum when the nomal of the loop is pependicula to the magnetic field, and zeo when the nomal is paallel to the field. ILsin since 90 IL The toque tends to cause the loop nomal to become aligned to the field, just like on a ba magnet. Cuent loop = magnetic dipole wsin IA sin Net toque IL Top view A Lw aea of loop magnetic moment m NIA sin numbe of tuns of wie

4 1.6 The Toque on a Cuent-Caying Coil 4 Example The Toque Exeted on a Cuent-Caying Coil A coil of wie has an aea of.0x10-4 m, consists of 100 loops o tuns, and contains a cuent of A. The coil is placed in a unifom magnetic field of magnitude 0.15 T. (a) Detemine the magnetic moment of the coil. (b) ind the maximum toque that the magnetic field can exet on the coil. (a) m magnetic moment 4 4 NIA A.0 10 m A m (b) magnetic moment NIA sin Am 0.15 Tsin Nm

5 1.6 The Toque on a Cuent-Caying Coil Application: The basic components of a dc moto. In Class Demo The bushes switches the diection of the cuent so that the toque is always in the same diection continuous otation 5

1.7 Magnetic ields Poduced by Cuents In Class Demo A LONG (), STRAIGHT WIRE

equies integal calculus o 4 10 7 T m A Magnitude pemeability of fee space

. Cul the finges of the ight hand into the shape of a half-cicle.

6 1.7 Magnetic ields Poduced by Cuents In Class Demo A LONG (), STRAIGHT WIRE caying cuent poduces a magnetic field o I Result to emembe: deivation equies integal calculus o T m A Magnitude pemeability of fee space Diection Right-Hand Rule No.. Cul the finges of the ight hand into the shape of a half-cicle. Point the thumb in the diection of the conventional cuent, and the tips of the finges will point in the diection of the magnetic field. 6

1.7 Magnetic ields Poduced by Cuents Example : A Cuent Exets a Magnetic oce on a Moving Chage The long staight wie caies a cuent of.0 A. A paticle has a chage of +6.

7 1.7 Magnetic ields Poduced by Cuents Example : A Cuent Exets a Magnetic oce on a Moving Chage The long staight wie caies a cuent of.0 A. A paticle has a chage of +6.5x10-6 C and is moving paallel to the wie at a distance of m. The speed of the paticle is 80 m/s. Detemine the magnitude and diection of the magnetic foce on the paticle. RHR CCW sense, seen fom top. RHR 1gives the foce towad qvsin oi the wie with magnitude ( fo an infinite staight wie gives oi qv sin 6 8 C)(80 m s ) N the field in the m (.0 A) C N m s A sin(90) (0.050 m) 7

1.7 Magnetic ields Poduced by Cuents Cuent caying wies can exet foces on each othe. Example: What is the attaction/epulsion foce pe mete of wie between two infinite staight wies caying 1.

8 1.7 Magnetic ields Poduced by Cuents Cuent caying wies can exet foces on each othe. Example: What is the attaction/epulsion foce pe mete of wie between two infinite staight wies caying 1.00A each, sepaated by 1.00 m? 1 L 1 0I1, I (4 10 0I1I I T m/a)(1.00 A)(1.00 A) (1.00 m) N s C m L C s 1 sin, N m 1 m This is in fact the oiginal SI definition of an ampee (A). 8

MAGNETIC FIELD INTRODUCTION

MAGNETIC FIELD INTRODUCTION It was found when a magnet suspended fom its cente, it tends to line itself up in a noth-south diection (the compass needle). The noth end is called the Noth Pole (N-pole),