ACP Magnetism Review
Name: ____________________
1. Sketch the magnetic field for the following bar magnet.
(The direction of a magnetic field is determined by the direction a NORTH compass
needle would point)
Very hard to draw w Word; they will be lines pointing from North toward South. None
cross.
N
S
2. What are the three grand ideas of magnetism?
-A current carrying wire produces a magnetic field
-A magnetic field exerts a force on a current carrying wire
-A changing magnetic field causes current to flow in a conductor
3. When current flows through a wire, what is produced? In what direction does this
“thing” travel?
A magnetic field is produced; it travels in a circle around the wire
4. A magnet is able to attract a paper clip, even though it is not magnetic. Explain why.
The magnet produces a magnetic field – the domains in the paper clip align themselves
with this, making it temporarily magnetic. As a result, the clip is attracted to the magnet
5. What is the ultimate source of all magnetic fields?
Moving electrons in atoms
6. Neon gas is diamagnetic. Explain what this means.
Diamagnetic means all the electrons in a substance are paired, so any magnetic field
produced by that atom is canceled.
7. Oxygen gas is paramagnetic. Explain what this means.
Oxygen has a few unpaired electrons, so the magnetic field produced by the atoms is not
completely canceled. However, it is still very weak.
8. Iron, nickel, and cobalt are all ferromagnetic metals. Explain what this means.
These metals all have many unpaired electrons, so they create stronger magnetic fields.
9. If iron is ferromagnetic, why isn’t all iron naturally a magnet?
Although iron atoms individually produce magnetic fields, a big piece of iron may not.
This occurs because each individual atom produces its own magnetic field, and these
magnetic fields often point in different directions, canceling out the overall field. In a
magnet, these fields, known as domains, all point in the same direction.
10. With electricity, we know that opposite charges attract. With magnetism, we know
that opposite poles attract. However, magnetic poles are different from electrical charges
in one major way. What is it?
Electrical charges can be isolated (ie. A positive charge can be on its own). Magnetic
poles are always in pairs (North and South). They cannot be isolated. Thus, they are
called dipoles.
11. Evaluate the following statement: “A compass is simply a piece of light-weight,
magnetized metal with the ability to turn freely in a container.” Is this correct? If not,
what is wrong with the statement?
This is essentially what a compass is. One side of the compass is attracted to Earth’s
North Pole, and thus always points in that direction.
12. Early navigators benefitted from the Earth’s magnetic field because they could use it
to determine the direction of north. However, the Earth’s magnetic field has been vital to
life for far longer than that. Why?
The magnetic field of the Earth deflects space radiation from reaching the surface of the
Earth. This radiation can be dangerous to life, as it can cause mutations that can lead to
cancers.
13. What is the reason that Earth’s magnetic field exists?
Molten iron in the Earth’s outer core is able to flow, creating electrical currents. These
currents produce the Earth’s magnetic field.
14. Is Earth’s magnetic North Pole at the exact geographic North Pole of the Earth?
No; in fact, it is constantly in motion due to the movement of the liquid iron in the Earth.
15. Will a stationary charge feel a force from a constant magnetic field?
No – a charge must be crossing magnetic field lines to feel a force. If both the charge and
the magnetic field are motionless, that cannot happen.
16. Look at the magnetic field below (labeled B). If the charge is moving to the left, will
it feel a force? If so, in what general direction (up/down, left/right, etc)? Explain.
B
It will not feel a force because it is not crossing magnetic field lines; it is going in a
parallel direction.
17. The magnetic field below is coming out of the page at you (each dot represents an
arrow head moving toward you). If the charge is moving toward the bottom of the paper,
will it feel a force? If so, in what general direction? Explain.



The charge will feel a force either to the left or right. This is the only direction not
covered by the moving charge or the magnetic field.
18. A motor armature is shown at the right with current flowing in a counter clockwise
direction around the wires as shown. A steady magnetic field is traveling to the right
across the armature.
A
B
a. If the right arm (segment BD) feels a push up as a result of this,
what type of push will the left arm (segment AC) feel? down
b. In what direction will the armature spin?
(clockwise / counter-clockwise / it won’t)
C
D
19. A motor’s primary purpose is to convert
electrical energy into mechanical energy.
20. The diagram below is of a generator. Give a general explanation for why rotating the
armature will cause electricity to flow.
When the armature rotates, the left and right arms move either up or down. The magnetic
field is moving to the right. So, the electrons that sit on the wire are “moving” up or down
(because the wire moves up or down); thus, they are crossing magnetic field lines. As a
result, they feel a force either “in” or “out”, and they move along the wire in that way.
21. This generator will produce what type of current? Alternating current (AC)
22. What is the primary purpose of a transformer?
To change the voltage of electricity.
23. The diagram below shows a transformer. Explain why such a device will not work if
the primary coil is powered by steady, direct current. (You may want to review the three
grand ideas of magnetism)
If direct current is used, it will
Create a magnetic field in the
Iron that is steady and unchanging.
According to the rules of magnetism,
there must be a changing magnetic
field to create current in the second coil.
Therefore, AC current must be used.
V1/V2 = n1/n2
V1I1 = V2I2
24. Electrical power is produced at a plant and transmitted at 140,000 V. It goes into a
transformer with 25 turns in its primary coil and 5 turns in its secondary coil. What will
the voltage be when it leaves the transformer?
28000 V
25. Electrical power enters a transformer with a voltage of 80 V and leaves with a
voltage of 120 V. If the transformer has 36 turns in its secondary coil, how many turns
are in the primary coil?
24 turns
26. Electricity enters a transformer with a voltage of 200 V and a current of 0.5 A. If it
leaves with a voltage of 1100 V, what will be its new current?
0.09 A
27. Electricity enters a transformer with a voltage of 8000 V and a current of 1.2 A. The
primary coil has 64 turns and the secondary coil has 18 turns. When the electricity leaves
the transformer, what will be its new voltage and current?
2250 V, which means the new current will be 4.27 A