Magnetism
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Transcript of Magnetism
Magnetism
Magnetic field- A magnet creates a
magnetic field in its vicinity.
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It represents the effect a magnet has on its surroundings.
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All magnetic fields arise from the motion of electric charge.
MagnetismMagnetic field lines can be used to represent magnetic fields.The closer the lines are together, the greater the magnitude of the vector B
Figure 22-4 Magnetic Field Lines for a Bar Magnet
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A magnetic field is represented by the symbol B
MagnetismThe direction of a magnetic field at a given location is the direction
in which the north pole of a compass points when it is placed in
that location.
B
MagnetismA charged particle moving in a
magnetic field will experience a force if it has a velocity component
perpendicular to the magnetic field.
Magnitude of the magnetic force FsinF q vB
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Magnitude of the magnetic field B1N SI unit = 1 tesla=1 T=
sin A•mFB
q v
MagnetismThe Magnetic Force Right
Hand Rule (RHR)
MagnetismTo find the direction of the magnetic force F, point your fingers in the direction of the velocity v.
Now curl them toward the direction of B.
Your thumb points in the direction of F.
Figure 22-8The Magnetic Force
Right-Hand Rule
Figure 22-9The Magnetic Force for Positive and Negative Charges
Conceptual Checkpoint 22-2Which is the positive? Negative? Zero charge?
MagnetismVelocity selector.
A device with both magnetic and electric fields present. Only charged particles moving with a certain speed will pass through undeflected.
Magnetism
The velocity that is undeflected is calculated byE v=B
Conceptual Checkpoint 22-3Which direction should the magnetic field be
to give zero force?
MagnetismA charged particle moving with a
velocity perpendicular to a uniform magnetic field, will move in a circle.
Figure 22-11The Electromagnetic Flowmeter
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2 2
Recall
a Fcp cpv mvr r
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2mvq vB=r
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mvr =q B
Figure 22-12Circular Motion in a Magnetic Field
Example 22-3Uranium Separation
•Forces on a long straight current carrying wire in a magnetic field.
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•Forces on a long straight current carrying wire in a magnetic field.
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•A long straight current carrying wire has charges moving inside it.
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•If it is placed in a magnetic field, it will experience a force
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MagnetismThe magnitude of the force is F = ILBsinWhere F is the magnitude of the forceB is the magnitude of the magnetic field
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L is the length of the wire in the magnetic field is the angle between the direction of the
magnetic field vector, and the direction of the current.
Figure 22-15The Magnetic Force on a
Current-Carrying Wire
Direction of magnetic forces in a current carrying loop in a
magnetic field.
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Figure 22-16Magnetic Forces on a Current Loop
Example 22-5Torque on a Coil
MagnetismThe magnitude of the torque is
= IABsinWhere is the torqueB is the magnitude of the magnetic fieldA is the area of the loop
MagnetismFor a loop of N turns,
= NIABsinWhere is the torqueB is the magnitude of the magnetic fieldA is the area of the loop
•To calculate the magnitude and direction of the magnetic field in the
vicinity of a long straight current carrying wire.
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Apply the magnetic field right hand rule.1. Point your thumb in the direction of
current flow.2. Curl your fingers around the wire 3. They will point in the direction of
the magnetic field.
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Figure 22-19The Magnetic Field
of a Current-Carrying Wire
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7
2 permeability of free space =
4 10
o
o
IBr
T mA
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