Mass Spectrometer
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Used to identify atoms
and their concentrations
in a sample of material.
Between S1 and S2,
molecules go straight if
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After S2, B produces
circular motion
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•
•
qE=qvB
or v = E/B
q v B’ = m v2/r
m = q B’ r/v = q B B’ r/E
Found isotopes
General Physics 2
Magnetism
1
E8 – Topics to cover
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•
•
•
•
Magnetic Force on a wire
Torque on a wire
Electric Motors - lab
Creating currents in moving loops
Eddy currents in moving conductors
General Physics 2
Magnetism
2
Force on a wire
•
Magnetic force of a straight wire segment
r
r r
Lr r
Fm,seg  I  bar  LI  B
c

General Physics 2
Magnetism
3
Demo: Magnetic Force
•
Interaction between B field and current
Moving charges are affected by B fields
General Physics 2
Magnetism
4
Force on Current in B Field
(for uniform field)
General Physics 2
Direction of F
•given by Right Hand Rule
•fingers = I
•bend fingers = B
•thumb = F
Magnetism
5
Think-Pair-Share
•
•
(a) What is the magnitude of the force per
meter of length on a straight wire carrying an
8.40-A current when perpendicular to a 0.90T uniform magnetic field?
(b) What if the angle between the wire and
field is 45.00?
General Physics 2
Magnetism
6
Torque on a wire
•
A loop carrying a current will experience a
torque which causes the loop to ROTATE!
r
rv r bar r r
  
  B
c
r
where mag  NAI
•
μ is the loop’s magnetic moment
•
Expresses the strength and south-to-north
orientation of the loop’s equivalent bar magnet
General Physics 2
Magnetism
7
Torque on a Loop
•
•
•
Forces on segments of a loop cause the loop to rotate
Simplify by replacing loop with magnet
•
Fingers in direction of current, thumb represents NORTH pole of
magnet
Think about the loop as a magnet will rotate so that the north face of
the magnet points in the direction of the magnetic field
General Physics 2
Magnetism
8
Electric Motors - Torque
•
In each orientation, which way will the loop
rotate?
•
Changing the direction of the current will keep
the loop spinning
General Physics 2
Magnetism
9
Commutator
•
To change the direction of the current and
keep the loop spinning, a commutator is used
•
http://www.walter-fendt.de/ph14e/electricmotor.htm
General Physics 2
Magnetism
10
Eddy currents in moving conductors
•
You can create a current in a metal plate by
moving the plate through a magnetic field.
•
Current density will be constant in the region
of the magnetic field
Fm  c vBbar
J  c

q
General Physics 2
c
Magnetism
11
Practice Problems
•
Magnetism: Worksheets 3 and 5
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Finish before next class
General Physics 2
Magnetism
12
Group Problems
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E8B.1
E8B.4
E8S.5
General Physics 2
Magnetism
13