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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley

Goals for Chapter 20

• To observe and visualize magnetic fields and forces.

• To study the motion of a charged particle in a magnetic field.

• To evaluate the magnetic force on a current-carryingconductor.

• To determine the force and torque produced with a magnetand current-carrying loop of wire (the DC motor.

• To study the fields generated by long! straight conductors.

• To observe the changes in the field with the conductor inloops (forming the solenoid.

• To calculate the magnetic field at selected points in space.

• To understand magnetism via magnetic moments.

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The behavior of bar magnets – Figures 20.2,20.3

• "otice the general behavior trends of attraction and repulsion!

dipole or monopole.

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Our Earth itself has a magnetic fiel. – Figure 20.!

• This field is not very strong but it is consistent (and convenient

as the ne#t slide will show.

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" compass #ill align #ith fiels – Figure 20.$

• The compass will align with

whatever average field is

strongest. $n figure %&.'! the

field caused by the current in the

wire is stronger than that any

bacground field from the earth.

• )bsent the current-carrying

wire! the compass would align

with the earth*s magnetic field.

This allows a consistent direction

to be determined by someonewith the need for navigation.

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(ron filings #ill align as a compass oes – Figure 20.)

• +ach small filing lines up tangent to the field lines

allowing a visual demonstration

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7/22Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley

The equipotential map around charges – Figure 18.11

• )round an charge or arrangement of charges regions of

equal potential may be drawn as equal-potential lines.

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Charges moving #ith respect to a fiel – Figure 20.*

• The effect of ane#isting

magnetic field on

a charge

depends on thecharges direction

of motion relative

to the field.

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The +ight an +ule – Figure 20.-0

,sing the right hand rule! one may determine the direction of the

field produced by a moving positive charge.

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The effect of the sign of a moving charge – Figure 20.--

ositive andnegative

charges will

feel opposite

effects from

a magnetic

field.

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&agnetic force ma be calculate – Figure 20.-3

efer to the Conceptual )nalysis! the roblem-/olving /trategy!

and +#ample %&.0 on pages 112 and 11' of your te#t.

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&agnetic fiels #ill alter ionic movement – Figure 20.-!

• 3ou can create

electrostatic lenses

that will focus or

alter the path or

velocity of ions or

electrons. This is

the foundation ofmodern mass

spectroscopy.

• efer to the

Conceptual )nalysison page 111 and

+#ample %&.4 on

page 15&.

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The &agnetron operating in our home – Figure 20.-/

• ) serendipitous discovery

of radar research! the

microwave oven uses amagnetron to trap

electronic oscillations with

wavelengths between .&&0

and 0&m.

• efer to Conceptual

)nalysis %&.4 on page 116

of your te#t.

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(ntrouction of helical motion – Figure 20.-'

• /uch motion can

be imparted to

ions given

velocities both

parallel and

perpendicular to

the applied field.

• efer to

Conceptual

)nalysis %&.2 and+#ample %&.% in

your te#t.

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Force on a conuctor #ith current – Figures 20.22, 23

• 7hen a

conductor!

often a wire!

carrying

current is

e#posed to

an e#ternal

magnetic

field! a force

is e#erted on

the

conductor.

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"pplications of force on a conuctor – Figures 20.2$,2/

• "ovel applications have been devised to mae use of the

force that a magnetic field e#erts on a conductor carrying

current.

• efer to Conceptual )nalysis %&.' and +#ample %&.2 in your

te#t.

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The motor – Figure 20.2'

• $f the conductor is a loop! the torque can create an electric

motor.

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&agnetic fiel of long straight conuctor – Figure 20.3!

• laced over a

compass! the wirewould cause the

compass needle to

deflect. This was the

classic demonstration

done by 8ersted as

he demonstrated the

effect.


)nalysis %&.5 and

+#ample %&.1

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Fiels in t#o conuctors siebsie – Figure 20.3/

• This was the classic demonstration done by )mpere as he

demonstrated the effect. efer to +#ample %&.5.

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Currents in a loop – Figures 20.3*, !0

• This will

allow usto

generate

a field

inside

loops ofconductor

carrying

current.

• efer to

+#ample

%&.6.

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&agnetic fiel of long straight conuctor – Figure 20.3!

• laced over a

compass! the wirewould cause the

compass needle to

deflect. This was the

classic demonstration

done by 8ersted ashe demonstrated the

effect.


)nalysis %&.5 and

+#ample %&.1

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Copyright © 2007 Pearson Education Inc publishing as Addison Wesley

The solenoi – Figure 20.!2

• 9enerating a

field inside acylinder which

already contains

a permanent

magnet will

cause a forceand move the

permanent

magnet.

• efer to

Conceptual

)nalysis %&.6.

phy2054-ppt20

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