cstephenmu
ay.com Copyright © 2010, C. Stephen Mu
ay
Magnetic Fields
Name: _____________________
Period: _____________________
Directions
Left Right Up Down Into page
Or “Forward”
Out of page
Or “Backwards”
Since paper is only two dimensional, we need symbols to show our three dimensional world.
Also, we use different words depending on our situation (on paper or in relation to your body).
Forwards and backwards come
from the tip and tail of an a
ow,
showing it coming towards you (a
point) or away from you (a cross).
Magnetic Fields
Magnetic fields are very similar to electric fields: they are a region in which a magnet
feels a force. We use the letter B as the variable for magnetic field.
Compasses
Compasses are small temporary magnets and very useful as indicators for magnetic fields.
A compass always points in the direction of the magnetic field.
N
The red side of a compass is
the north pole of its magnet.
We will use an a
ow to
show the red side.
S
N
S
A compass always
points towards a
south pole or away
from a north pole.
B
A magnet (or compass) will turn
to align with the magnetic field.
N
S
N
S
Field lines always point from North to South
and are stronger closer to the poles.
N
S
Moves
ight
Moves
left
B shows the direction a north
pole of a magnet will move.
I
B
A straight cu
ent ca
ying wire
creates a circular magnetic
field. With your thumb in the
direction of the positive cu
ent
flow, your fingers coil in the
direction of the magnetic field.
Circular cu
ents (as in a solenoid)
produce straight magnetic fields.
With your fingers curled in the
direction of the positive cu
ent
flow, your thumb points in the
direction of B.
B
I
Cu
ent Ca
ying Wires
Electricity causes magnetism. Using the right-hand rule you can find the direction of B.
Remember that the direction of the cu
ent is for positive (conventional) cu
ent flow.
turns
ed
Iout Iin
(into page)
A solenoid N
+
(red)
(out of page)
– (black) (red) +
I
–
(black)
I (cu
ent)
A
w
i
e
–
(
lack
)
(red
) +
I
I
I
cstephenmu
ay.com Copyright © 2010, C. Stephen Mu
ay
1. Using the first compass as an
indicator, label the poles of the
magnet and fill in the other
compasses.
2. A. Label the N and S sides of
the magnetic field (B).
B. Fill in the compasses.
4. What happens to two compasses that are put together?
6. A) Draw the magnetic field lines around the magnets.
B) Fill in the compasses.
I
9. A) Draw the direction the compasses would point due to the
cu
ent ca
ying wire.
B) Which direction is B on the right side of the wire?
(And draw it with the symbols given on the front).
B
3. What is the direction of B (magnetic field) in these situations?
A) C)B)
7. A) Draw the direction of B
between the magnets.
B) Which way will the
compass turn?
N
S
N
S
5. A) Draw the direction of B between the magnets.
B) Which way will the compass turn?
N
S N
S
8. Positive cu
ent is hooked up to side 2 (goes in 2),
A) Which side is north?
B) Fill in the compasses
2 1
I
10. Positive cu
ent is hooked up to side 2 (goes in 2).
A) Which side of the solenoid is north?
B) Fill in the compasses.
11.A) Which direction is B on
the right side of the wire?
B) Which direction is B
on the left side?
C) Using the right-hand-rule,
determine the direction the
cu
ent must be flowing in the wire.
Side-by-side On top of each other
N
S
N
S
A wire
B
12. A) If the diagram shows a wire with cu
ent
coming out of the page, draw B around
the wire.
B) Is B clockwise or counterclockwise?
13. A) Is the cu
ent in the wire moving
clockwise or counterclockwise?
B) Which direction is the magnetic field
pointing inside the loop?
I
I
1 2