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Sierzega: Magnetism 1
Are Electricity and Magnetism Related?
1.1 Observe and find a pattern
Using the tiny compasses spread them out on a table. Notice that they all point towards Earth’s
geographical north. Now, place a bar magnet in the middle of the compasses.
a. Draw a picture of the magnet and the orientation of each compass below.
b. Describe in words a pattern between the orientation of the magnet’s poles and the
orientation of the compass.
1.2 Observe and find a pattern
How do the iron filings appear around the magnet? Draw a picture.
Is this consistent with the pattern you developed using the tiny compasses?
The magnetic B-field and its representation by B-field lines
 The direction of the magnetic B-field at a point is defined as the direction of a compasses
north pole when at that point.
 Magnetic field lines represent the B-field.
 The B-field vector at a point is tangent to the direction of the B-field at that point.
 The density of lines in a region represents the magnitude of the B-field in that region–where
the B-field is stronger, the lines are closer together.
Sierzega: Magnetism 1
1.3 Draw the B-field lines for the following bar magnet orientations:
a. One magnet
b. North pole – north pole
S
N
S
c. South pole – north pole
N
S
N
N
S
d. South pole – south pole
N
N
S
S
S
N
N
Do any other objects besides magnets create magnetic fields? We
found earlier that stationary electrically charged objects do not, but
maybe moving electric charges do…
1.4 Observe and find a pattern
In order to determine whether electric currents produce magnetic fields,
connect a battery and some wires. Make sure that one of the wires in the
circuit is aligned along the geographical north-south direction. Place a
compass below a north-south oriented wire with the battery
disconnected from the circuit; there is no current in the circuit. The
needle points north.
https://www.youtube.com/watch?v=PB4tHSagdng
Direction of the
current
Current flows in the
north-to-south direction
in the wire.
If you reverse the
battery poles, the
current now flows in a
south-to-north direction
in the wire above or
below the compass.
Draw an arrow
representing the
orientationof the
compass when placed
below the wire.
Draw an arrow
representing the
orientation of the
compass when placed
above the wire.
A
B
Sierzega: Magnetism 1
a. Use the thumb of your right hand to represent the direction of the current and your
four fingers of the same hand to represent the direction of the compass. Does the
orientation of your thumb and fingers describe a pattern between the direction of the
current and the orientation of the compass for all of the above experiments?
b. Come up with a reason why electric current (moving electrically charged particles) might
affect the behavior of magnets differntly than would stationary charged objects.
1.5 Draw magnetic field lines for a coil when it is connected to a battery. How do the B-field
lines compare to those for a bar magnet?
1.6 Draw magnetic field lines for a solenoid when it is connected to a battery. How do the B-field
lines compare to those for a bar magnet?
1.7 Draw the B-field lines for each section of the following circuits:
Sierzega: Magnetism 1
1.8 Use the right hand rule for the B-field and the superposition principle to predict the direction
of the magnetic field exactly in the middle between two straight wires oriented horizontally
in the plane of the page. The current through the top wire is toward the right and the current
through the bottom wire is toward the left.
1.9 What is the direction of the B-field at a point that is exactly in the middle between two
straight wires with currents in the same direction?
1.10 Imagine that a wire passes up through the page you are reading. Iron filings are sprinkled
on the page. We can think of the iron filings as small compasses. Draw a picture showing the
filings when no current is moving in the wire. Then draw a picture of the arrangement of the
filings when there is a significant current in the wire.
a. Is your picture consistent with the results of the experiment above? Explain your answer.
b. Draw a sketch that you think represents the orientation of magnetic field vectors produced
by the electric current in the wire at five different points. (Hint: Choose the direction of
the current out of the page.)
1.11 Current flows in each of the wires shown in the illustration. Determine the direction of the
magnetic field created by the current at the points indicated and draw it with an arrow, a dot
(out of the page), or an “×” (into the page). The objects indicated in the illustration are
sources of magnetic field.
(a)
(b)
(c)
A .
A
.
B
.
C
.
A
.
B
.
C
.
D
.
B .
C.
E .
I
I
E .
I
. D