Transcript MAGNETIC FIELDS

MAGNETIC FIELDS
Pre-Class for Wednesday 5-2-12
True or False: Electricity and
Magnetism are related.
• Begin next chapter: Ch24: Magnetic
Fields
– Brief history of magnets
Some Definitions
• Magnetic Force
– The interaction when two
magnets are brought close
together
– Can be attraction or
repulsion
• Magnetic Field
– Represents the effect of a
magnet on the area around it
• Magnetic Poles
– Two for every magnet
– Strongest field found here
– North (out) and South (in)
Observing
Magnetic
Interference
Equipment needed:
paper clip, ring stand,
clamp, bar magnet, string
Material tested Result
Paper
Fabric
Scissor blade
Aluminum foil
Other:
Procedures
a. Clamp a bar magnet
vertically to the ring
stand.
b. Tie string around a
paper clip.
c. Anchor the end of the
string under a book.
Slowly pull the string
until the paper clip
floats in the air.
d. Without touching the
paper clip, slide
various objects
between the magnet
and paper clip.
e. Record observations
Pre-class for Thursday
5-3-12
The location of the strongest magnetic field on a
magnet is at the _____.
A. Magnetic force
B. Magnetic poles
C. Magnetic domains
D. Electromagnets
Why a magnetic field?
• The mantle is on a
tectonic plate, which
floats on a river of liquid
rock/metal
• The magma is flowing,
just like a river
• Friction between the
plates and magma cause
charges to move,
creating a magnetic field
MAGNETIC FORCE DUE TO A
CURRENT-CARRYING WIRE
F=BIL
F  force of magnetic field (N)
B  magnetic field strength (T or gauss)
I  current in wire (Amp)
L  length of wire (m)
#1 Right Hand Rule
B field
I
• Fingers point
direction of magnetic
field (curved around
the wire)
• Thumb point
direction of current
MAGNETIC FORCE DUE TO A
CHARGED PARTICLE IN A
MAGNETIC FIELD
F=qvB
F
q
v
B
magnetic force (N)
charge (C)
velocity (m/s)
magnetic field (T or gauss)
#2 Right Hand Rule
• Fingers point
direction of magnetic
field
• Thumb point
direction of motion for
the particle
• Force on charge due to
magnetic field comes
out of the palm
Works for positive charges only!!!(use left hand for negative)
B field
P+
e-
X F
F
What direction will the force be?
B field
P+
e-
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
F
F
What direction will the force be?
Pre-class for Monday
5+7=12
Objects that keep their magnetic properties for a long
time are called _____.
a. Permanent magnets
b. Electromagnets
c. Magnetic domains
d. Temporary magnets
CH 24 HW
CH 25 HW
59. move left or spin
63. 0.04 T
65. ccw
66. into page; out of
page
74. 2.4 N
78. 3000 Amps
84. .742 T; 2.66x1016
m/s2
92. 2.1x10-12 N, upward
60. 0.5 T
61. 0.89 Volts
73. 0.13 Volts; 0.13
Amps; cw; opposite
75. 1,800 Volts; 30
Amps; 3,600 Watts
76. 36 turns; 9.4 mAmps
77. 2:1; 5 Amps
80. 3600 Volts, 90 Amps;
1.1x104 Watts
Electromagnetic Induction
The process of producing a current in
a wire using magnetism
Electromagnet
• A magnet produced by
current electricity
• No current, no magnet
• Wire must be wrapped
to combine the magnetic
field produced
• A metal (Iron, etc.) core
can help, but is not
necessary
• How magnets are made
Making Your Own Electromagnet
• Materials
–
–
–
–
–
Wire
Battery
10 paper clips
Nail or bolt
Christmas light
# of turns # of paper
of wire
clips
5
10
20
30
• Procedures
– Make an electromagnet
– Do not complete the
circuit until you are
ready! Battery will get
hot!
– Fill out the chart with
the proper number of
turns and paper clips.
• Objective
– Construct an
electromagnet and pickup paper clips.
Electromotive Force
• The voltage produced by a battery to move
energy around a wire
• It is not a force—it was named this because
it was originally thought charges were being
“forced” to move around a wire
• Units: Volts
EMF = B l v sinq
Pre-class for Tuesday
5-8-12
Find the direction of the
magnetic field on the
inside and outside of
the solenoid shown.
2 TYPES OF CURRENT
• Alternating (AC) Current
– Current changes direction
– Current flows both ways
• Direct (DC) Current
– Current flows one direction only
– Defined by Ohm’s Law
But, not these
Transformers!!!
TRANSFORMERS
• A device used to increase
or decrease the voltage in
an AC circuit
• 2 basic types
– Step-up: increase voltage
– Step-down: decrease voltage
• Used to change the voltage
sent from the power
company to your house
CH 24 HW
CH 25 HW
59. move left or spin
63. 0.04 T
65. ccw
66. into page; out of
page
74. 2.4 N
78. 3000 Amps
84. .742 T; 2.66x1016
m/s2
92. 2.1x10-12 N, upward
60. 0.5 T
61. 0.89 Volts
73. 0.13 Volts; 0.13
Amps; ccw; opposite
75. 1,800 Volts; 30
Amps; 3,600 Watts
76. 36 turns; 9.4 mAmps
77. 2:1; 5 Amps
80. 3600 Volts, 90 Amps;
10800 Watts for both
Pre-class for Wednesday 5-9-12
The function of an electric motor is to _____.
a)
b)
c)
d)
Change electrical energy to chemical energy
Change chemical energy to electrical energy
Change mechanical energy to electrical energy
Change electrical energy to mechanical energy
• Materials
–
–
–
–
Electric Motor or
Generator
Battery
Hand crank generator
Light bulbs
Switch
• Objective
– To make an electric motor and
generator
• Questions
– Which part models an electric
motor? Explain.
– Which part models an electric
generator? Explain.
– What would happen if a battery
with a larger voltage was used?
– Where is the magnetic field the
strongest? Explain.
Procedures
A. Connect the hand generator, light
bulb, and switch in series. Turn
the hand crank and record the
light bulb brightness.
B. Remove hand generator and
connect battery instead. Record
light bulb brightness.
C. Connect battery to hand
generator and switch. Close
switch. Record observations.