Download Figure 22-4 Magnetic Field Lines for a Bar Magnet

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Transcript
Magnetism
Magnetic fieldA magnet creates a
magnetic field in its vicinity.
Magnetism
It represents the effect a
magnet has on its
surroundings.
Magnetism
All magnetic fields arise
from the motion of
electric charge.
Magnetism
Magnetic 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
Magnetism
A magnetic field is
represented by the
symbol B
Magnetism
The direction of a magnetic field B
at a given location is the direction
in which the north pole of a
compass points when it is placed in
that location.
Magnetism
A 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 F
F  q vB sin 
Magnetism
Magnitude of the magnetic field B
F
1N
B
SI unit = 1 tesla=1 T=
q v sin 
A•m
Magnetism
The Magnetic Force Right
Hand Rule (RHR)
Magnetism
To 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 22-8
The Magnetic Force
Right-Hand Rule
Figure 22-9
The Magnetic Force for Positive and Negative Charges
Conceptual Checkpoint 22-2
Which is the positive? Negative? Zero charge?
Magnetism
Velocity 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 by
E
v=
B
Conceptual Checkpoint 22-3
Which direction should the magnetic field be
to give zero force?
Magnetism
A charged particle moving with a
velocity perpendicular to a uniform
magnetic field, will move in a circle.
Figure 22-11
The Electromagnetic Flowmeter
Magnetism
Recall
2
v
a cp 
r
mv
Fcp 
r
2
Magnetism
mv
q vB=
r
2
Magnetism
mv
r=
qB
Figure 22-12
Circular Motion in a Magnetic Field
Example 22-3
Uranium Separation
Magnetism
•Forces on a long straight
current carrying wire in a
magnetic field
.
Magnetism
•Forces on a long straight
current carrying wire in a
magnetic field
.
Magnetism
•A long straight current
carrying wire has charges
moving inside it.
Magnetism
•If it is placed in a magnetic
field, it will experience a
force
Magnetism
The magnitude of the force is
F = ILBsin
Where F is the magnitude of the force
B is the magnitude of the magnetic field
Magnetism
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 22-15
The Magnetic Force on a
Current-Carrying Wire
Magnetism
Direction of magnetic
forces in a current
carrying loop in a
magnetic field.
Figure 22-16
Magnetic Forces on a Current Loop
Example 22-5
Torque on a Coil
Magnetism
The magnitude of the torque is
 = IABsin
Where  is the torque
B is the magnitude of the magnetic field
A is the area of the loop
Magnetism
For a loop of N turns,
 = NIABsin
Where  is the torque
B is the magnitude of the magnetic field
A is the area of the loop
Magnetism
•To calculate the magnitude and
direction of the magnetic field in the
vicinity of a long straight current
carrying wire.
Magnetism
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.
Figure 22-19
The Magnetic Field
of a Current-Carrying Wire
Magnetism
o I
B
2 r
o  permeability of free space =
T m
4  10
A
7
Magnetism