PHY2054-PPT20
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Transcript of PHY2054-PPT20
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8/9/2019 PHY2054-PPT20
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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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
" 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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
(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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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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10/22Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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8/9/2019 PHY2054-PPT20
11/22Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
&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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
(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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
"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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
The motor – Figure 20.2'
• $f the conductor is a loop! the torque can create an electric
motor.
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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
&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.
• efer to Conceptual
)nalysis %&.5 and
+#ample %&.1
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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
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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Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley
&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.
• efer to Conceptual
)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.