2/26/2014. Magnetism. Chapter 20 Topics. Magnets and Magnetic Fields. Magnets and Magnetic Fields. Magnets and Magnetic Fields

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Magnets and Magnetic ields Magnetism Howee, if you cut a magnet in half, you

ectue otes Chapte 20 Topics Magnets and Magnetic ields Magnets and Magnetic

Magnetic ield oce on Electic Chage Moing in a Magnetic ield Magnetic ield Due

Magnetic fields can be isualized using magnetic field lines, which ae always

Magnets and Magnetic ields Magnets and Magnetic ields Magnets hae two ends

1 Magnets and Magnetic ields Magnetism Howee, if you cut a magnet in half, you don t get a noth pole and a south pole you get two smalle magnets. ectue otes Chapte 20 Topics Magnets and Magnetic ields Magnets and Magnetic ields Electic Cuents Poduce Magnetic ields oce on an Electic Cuent in a Magnetic ield oce on Electic Chage Moing in a Magnetic ield Magnetic ield Due to a ong Staight Wie oce between Two Paallel Wies Solenoids and Electomagnets Magnetic fields can be isualized using magnetic field lines, which ae always closed loops. Magnets and Magnetic ields Magnets and Magnetic ields Magnets hae two ends poles called noth and south. ike poles epel; unlike poles attact. A unifom magnetic field is constant in magnitude and diection. The field between these two wide poles is nealy unifom. 1

Electic Cuents Poduce Magnetic ields Expeiment shows that an electic cuent poduces a magnetic field.

This equation defines the magnetic field. Unit of : the tesla, T. 1 T 1 A m Electic Cuents Poduce Magnetic ields The diection of the field is gien by a ight-hand ule.

sin When the cuent is pependicula to the magnetic field. oce on an Electic Cuent in a Magnetic ield A magnet exets a foce on a cuent-caying wie. The diection of the foce is gien by a ight-hand ule.

2 Electic Cuents Poduce Magnetic ields Expeiment shows that an electic cuent poduces a magnetic field. oce on an Electic Cuent in a Magnetic ield The foce on the wie depends on the cuent, the length of the wie, the magnetic field, and its oientation. sin The foce is diected into the sceen. This equation defines the magnetic field. Unit of : the tesla, T. 1 T 1 A m Electic Cuents Poduce Magnetic ields The diection of the field is gien by a ight-hand ule. oce on an Electic Cuent in a Magnetic ield The foce on the wie depends on the cuent, the length of the wie, the magnetic field, and its oientation. sin When the cuent is pependicula to the magnetic field. oce on an Electic Cuent in a Magnetic ield A magnet exets a foce on a cuent-caying wie. The diection of the foce is gien by a ight-hand ule. oce on an Electic Cuent in a Magnetic ield Poblem A 1.5-m length of wie caying 4.5 A of cuent is oiented hoizontally. At that point on the Eath s suface, the dip angle of the Eath s magnetic field (5.5 x 10-5 T) makes an angle of 38 to the wie. Estimate the magnitude of the magnetic foce on the wie due to the Eath s magnetic field of at this point. sin ( 4.5 A)( 1.5 m)( 5.5 x 10 T ) sin 38 5 e 2.3 x

3 oce on an Electic Cuent in a Magnetic ield Poblem Suppose a staight 1.00-mm-diamete coppe wie could just float hoizontally in ai because of the foce due to the Eath s magnetic field which is hoizontal, pependicula to the wie, and of magnitude What cuent would the wie cay? e mg 2 d e ρπ g 2 e mg oce on Electic Chage Moing in a Magnetic ield Poblem Alpha paticles of chage +2e and mass of 6.6 x kg ae emitted fom a adioactie souce at a speed of 6.6 x 10 7 m/s. What magnetic field stength would be equied to bend them into a cicula path of adius of 0.25 m? M q ρπd2g 4e 8.9 x 10 3 kg 3 ( m) 2 π 1.0 x 10 2 m 5 4( 5.0 x 10 T ) g m 27 7 ( 6.6 x 10 kg )( 6.6 x 10 m/s ) 19 2( 1.6 x 10 C)( 0.25 m) q 5.4T 1400 A oce on Electic Chage Moing in a Magnetic ield The foce on a moing chage in a magnetic field is elated elated to its chage and elocity. q sin The foce is diected out of the sceen. Once again, the diection is gien by a ight-hand ule. q oce on Electic Chage Moing in a Magnetic ield Poblem Detemine the magnitude and diection of the foce on an electon taeling hoizontally 8750 m/s, to the east in a etically upwad magnetic field of stength 0.75 T. noth Diection? M q ( 1.6 x C)( 8.75 x 10 m/s)( 0.75T) 3 M east M x 10 oce on Electic Chage Moing in a Magnetic ield oce on Electic Chage Moing in a Magnetic ield f a chaged paticle is moing pependicula to a unifom magnetic field, its path will be a cicle. q q q m Momentum q Poblem What is the elocity of a beam of electons E that go undeflected when passing though pependicula electic and magnetic fields of magnitude 8.8 x 10 3 V/m and 3.5 x 10 3 T, M espectiely? What is the adius of the electon obit if the electic field is tuned off? E M q M m qe q q E 8.8 x 103 V/m 3.5 x 10 3 ( 9.11 x kg)( 2.5 x 106 m/s) T 1.6 x C 3.5 x 10 3 T 2.5 x 106 m/s ( )( ) 4.1 x 10 3 m 3

Magnetic ield Due to a ong Staight Wie The field is inesely popotional to the distance fom the wie: p µ o 2π The constant µ 0 is called the pemeability of fee space, and has the alue: µ 4π x 10 7 o T

4 Magnetic ield Due to a ong Staight Wie The field is inesely popotional to the distance fom the wie: p µ o 2π The constant µ 0 is called the pemeability of fee space, and has the alue: µ 4π x 10 7 o T m/a oce between Two Paallel Wies The magnetic field poduced at the position of wie 2 due to the cuent in wie 1 is: µ o 1 1 2π d The foce this field exets on a length of wie 2 is: 2 1 µ o 1 1 2π d µ o 1 2 2π d Magnetic ield Due to a ong Staight Wie Poblem A jumpe cable used to stat a stalled ehicle caies a 65-A cuent. How stong is the magnetic field 6.0 cm away fom it? p µ o ( 4π x10 7 T m/a)( 65 A) 2π 2π ( 6.0 x10 2 m) oce between Two Paallel Wies Paallel cuents attact; anti-paallel cuents epel x10 4 T Magnetic ield Due to a ong Staight Wie Poblem A powe line caies a cuent of 95 A along the tops of 8.5 m-high poles. What is the magnitude of the magnetic field poduced by this wie at the gound? µ o ( 4π x10 7 T m/a)( 95 A) 2π 2π ( 8.5 m) 2.2 x10 6 T Poblem Detemine the magnitude and diection of the foce between two paallel wies 35 m long and 6.0 cm apat, each caying 25 A in the same diection. µ o 1 2 2π d oce between Two Paallel Wies ( 4π x T m/a)( 25 A) ( 35 m) 2π 6.0 x x10 2 m ( ) d 4

Solenoids and Electomagnets Summay A solenoid is a long coil of wie.

cuents poduce magnetic fields A magnetic field exets a foce on an electic cuent: A magnetic field exets a foce on a moing chage sin qsin Poblem 20-48 Solenoids and Electomagnets A

12 m) Summay Magnitude of the field of a long, staight cuent-caying wie Magnetic field inside a solenoid µ o 2π Paallel cuents attact; anti-paallel cuents epel µ o 8.

5 Solenoids and Electomagnets Summay A solenoid is a long coil of wie. f it is tightly wapped, the magnetic field in its inteio is almost unifom: µ o Magnets hae noth and south poles ike poles epel, unlike attact Unit of magnetic field: tesla Electic cuents poduce magnetic fields A magnetic field exets a foce on an electic cuent: A magnetic field exets a foce on a moing chage sin qsin Poblem Solenoids and Electomagnets A thin 12-cm-long solenoid has a total of 420 tuns of wie and caies a cuent of 2.0 A. Calculate the field inside nea the cente. µ o ( 4π x10 7 T m/a)( 2.0 A)( 420) ( 0.12 m) Summay Magnitude of the field of a long, staight cuent-caying wie Magnetic field inside a solenoid µ o 2π Paallel cuents attact; anti-paallel cuents epel µ o 8.8 x10 3 T oce between to long staight cuents. µ o 1 2 2π d Poblem Solenoids and Electomagnets A 30.0-cm-long solenoid 1.25 cm in diamete is to poduce a field of T at its cente. How much cuent should the solenoid cay if it has 975 tuns of the wie? µ o µ o ( T)( m) ( 4π x10 7 T m/a)( 975) 94.3 A 5

Physics Spring 2012 Announcements: Mar 07, 2012

Physics Spring 2012 Announcements: Mar 07, 2012 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