Download Magnetic field

A magnet is a
material or object
that produces a
magnetic field with
a North and South
Pole.

Magnetism:
an
invisible force that
pushes or pulls
magnetic material.
H
I
S
T
O
R
Y
O
F
M
A
G
N
E
T
S



Regions of atoms
that have the same
magnetic polarity
(N/S Alignment).
Mini-magnets.
Unmagnetized Iron



Magnetic domains
point in different
directions.
Magnetic fields
cancel each other
out.
Magnetized Iron


Magnetic domains are
lined up in the same
direction
Magnetic fields
amplify each other.
The direction of the magnetic
force is from NORTH to SOUTH
TWO UNLIKE POLES
GIVE A FORCE OF
ATTRACTION
Can you explain what the
lines of force show?
Where is the strongest
part of the field?
Where is the weakest
part of the field?
TWO LIKE POLES
TOGETHER WILL HAVE
A FORCE OF
REPULSION
Small particles of iron filings are pushed
into patterns by a magnetic field. If we
sprinkle iron filings on a piece of paper
over a magnet we can see...
The lines of force are
very close together
here – the field is very
strong.
The lines of force are
further apart here –
the field is weaker.
A line of force links one pole of a magnet to the
other pole.
FOR EACH PICTURE IDENTIFY THE FORCE
ILLUSTRATED……………
A)
B)
MAGNETIC COMPASS
CONTAINS A MAGNET
THAT INTERACTS WITH
THE EARTH'S
MAGNETIC FIELD AND
ALIGNS ITSELF TO
POINT TO THE
MAGNETIC NORTH
AND SOUTH POLES.
North magnetic
pole located at
south
geographic
pole
South magnetic
pole located at
north
geographic
pole.
Magnetic declination
•is the angle between
magnetic north and
geographic true
north.
•Angle varies by
location
•Ranges from 0⁰ to 25 ⁰
Electromagnet

coil of wire that acts as a
magnet when an Electric
current is passed through
it.

stops being a magnet when the
current stops.

Often, the coil is wrapped
around a core of
ferromagnetic material like
steel, this enhances the
coils magnetic field.
an object made from a
material that is
magnetized
&
creates its own
persistent magnetic
field.

Example
refrigerator magnet
 Levitating
trains
(MagLev)
 Treat
depression
& chronic
headaches
 Electric
 Stereo
 Credit
motors
Speakers
Cards
•Produced by electric currents
•Defined as a Region where magnetic forces
can be detected.
•Has a North & South magnetic pole
•The SI unit for a large magnetic field is the
Tesla
•The SI unit for a smaller magnetic field is the
Gauss
•(1 Tesla = 10,000 Gauss).
The strength of a magnetic field (B)
is related to the amount of magnetic
force (F) that is applied to a moving
test charge when it is at a given
location in the field.
B = F magnetic
qv
q = test charge magnitude
v = speed of the charge
A proton moving east experiences an upward force of 8.8 x
10-19 N due to the Earth’s magnetic field. The field has a
strength of 5.5 x 10-5 Teslas (T) to the north.
Find the speed of the proton.
q = 1.60 x 10-19 C
B = 5.5 x 10-5 T
Fmagnetic = 8.8 x 10-19 N
B = Fmagnetic
qv
v = Fmagnetic
qB
Fmagnetic = qvb SinѲ
Solution
v =
8.8 x 10-19 N
(1.60 x 10-19 C) (5.5 x 10-5 T)
1.0 x 10 5 m/s
The direction of
the magnetic force
is perpendicular to
the plane of the
magnetic field and
to the direction of
the charge.
USE THE RIGHT
HAND RULE!!!
I – CURRENT
Current carrying wires that are
placed in a magnetic field also
experience a magnetic force.
F- FORCE
WIRE
The magnitude of the magnetic
force can be written in terms of
the current (I) flowing through
the length of the wire (L).
Magnetic Force in a Current
Carrying wire
F = BIL
A 10.0 m long power line carries a current of 20.0 A
perpendicular to the Earth’s magnetic field of
5.5 x 10-5 T.
What is the magnetic force experienced by the power
line?
I = 20.0 A
B = 5.5 x 10-5 T
L = 10.0 m
F = BIL
F = (5.5 x 10-5 T)(20.0 A)(10.0 m) = 0.011 N
Charges that are in motion (an electrical
current) produce magnetic fields.
Magnetic field moves
around a wire with a
current in a
circular fashion.
Which direction???
Right Hand Rule
1. Thumb goes in the
direction of the current.
2. Fingers wrap around
wire in the direction of
the magnetic field.
Arranging wire in a coil and running a
current through produces a magnetic
field that is similar to a bar magnet.
•A
coil
wound into
a tightly
packed
helix.
•Produces a
uniform
magnetic
field when
a charge is
applied to
it.
1. A particle with a positive charge of q moves with a speed v and passes
through a magnetic field B parallel with the speed v. What is the magnitude
of the magnetic force on the particle?
a) F = qvB
b) F = -qvB
c) F = 0
d) F = qvB/2
e) F = -qvB/2
2. In the figure below, a magnetic field of .01 T is applied locally to a wire
carrying a current of intensity I = 10A. What is the magnitude of the
magnetic force applied to the wire?
a) F = .3N
b) F = .4N
c) F = .5N
d) F = 1N
e) F = 3N

A wire 36 m long carries a current of 22A from east to west. If the
maximum magnetic force on the wire at this point is
downward(toward Earth) and has a magnitude of 4.0 X 10-2 N, find
the magnitude and direction of the magnetic field at this location.


Given: l = 36 m I = 22A Fmagnetic = 4.0 X 10 -2 N
Unknown: B = ???

Fmagnetic = B ∙ I ∙ l
then
B = Fmagnetic
Il
B=
1. A particle with a positive charge of q moves with a speed v and passes through a magnetic field B parallel with the speed v. What is
the magnitude of the magnetic force on the particle?
a) F = qvB
b) F = -qvB
c) F = 0
d) F = qvB/2
e) F = -qvB/2
Solution: c)
The force F, on the charge q moving with a velocity v in a magnetic field b is F = q(v x B).
The magnitude of F is F = q·v·B·sinθ where θ is the angle between v and B.
In our case the v and B vectors are parallel, so sinθ = 0. In conclusion F = 0.
2. In the figure below, a magnetic field of .01 T is applied locally to a wire carrying a current of intensity I = 10A. What is the magnitude
of the magnetic force applied to the wire?
a) F = .3N
b) F = .4N
c) F = .5N
d) F = 1N
e) F = 3N
Solution: b)
The magnitude of a magnetic force applied to a current-carrying wire situated in a magnetic field is
F = I·B·l·sinθ
where:
·
·
·
·
l is the length of the wire,
B is the magnetic field strength
I is the current in the wire,
θ is the angle between the wire and the magnetic field.
In our case sinθ = 4/l so l·sinθ = 4m.
F = 10A·.01T·4m = .4N

A wire 36 m long carries a current of 22A from east to
west. If the maximum magnetic force on the wire at this
point is downward(toward Earth) and has a magnitude of
4.0 X 10-2 N, find the magnitude and direction of the
magnetic field at this location.


Given: l = 36 m I = 22A Fmagnetic = 4.0 X 10 -2 N
Unknown: B = ???

Fmagnetic = B ∙ I ∙ l
then
B = Fmagnetic
Il
B = 4.0 X 10-2 N = 5.0 X 10-5 T
(22A)(36m)