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MST ST-589D Electromagnetism and Light
Cynthia Dumayas
Sonnenfeld
MST Student # 900312033
Prof. Richard
Review Questions – page 241
1. By whom, and in what setting, was the relationship between
electricity and magnetism discovered?
Hans Christian Oersted discovered, in a classroom demonstration, that an
electric current affects a magnetic compass. In his demonstration he saw
that magnetism was related to electricity.
2. In what way is the rule for the interaction between magnetic
poles similar to the rule for the interaction between electric
charges?
A magnetic force is similar to an electrical force, in that a magnet can both
attract and repel without touching and the strength of its interaction depends
on the distance between magnets. Whereas electric charges produce
electrical forces, regions called magnetic poles give rise to magnetic forces.
“Like poles repel; opposite poles attract.” This rule is similar to the rule for
the forces between electric charges, where like charges repel one another
and unlike charges attract.
3. In what way the magnetic poles very different from electric
charges?
Whereas electric charges can be isolated, magnetic poles cannot. Electrons
and protons are entities by themselves.
4. What produces a magnetic field?
A magnetic field is produced by the motion of electric charge.
5. What two kinds of motion are exhibited by electrons in an
atom?
Two kinds of electron motion produce magnetism: electron spin and electron
revolution.
6. What is a magnetic domain?
A clusters of aligned atoms.
7. Why is iron magnetic and wood not?
Iron, unlike wood, has magnetic domains that can be induced into alignment.
8. Why will dropping an iron magnet on a hard floor make it a
weaker magnet?
If a permanent magnet is dropped on a hard floor it sudden changes in
motion can jostle atoms out of alignment.
9. What is the shape of a magnetic field about a current carrying
wire?
The magnetic field about the current-carrying wire makes up a pattern of
centric circles.
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10.What happens to the direction of the magnetic field about an
electric current when the direction of the current is reversed?
When the current reverses direction, the compass needles turn around,
showing that the direction of the magnetic field changes also.
13. In what direction relative to a magnetic field does a charged
particles move in order to experience maximum deflecting force?
Minimum deflecting force?
A charged particle at rest will not interact with a static magnetic field.
However, if the changed particle moves in a magnetic field, the magnetic
character of a charge in motion becomes evident: The charged particle
experiences a deflecting force. The force is greatest when the particle moves
in a direction perpendicular to the magnetic field lines.
14. Both gravitational and electrical forces act along the direction of
the force fields. How does the direction of the magnetic force on
moving charged particles differ?
The direction of the magnetic force is always perpendicular to both the
magnetic field lines and the velocity of the charged particle.
16. Since a magnetic force acts on a moving charged particle, does
it make sense that a magnetic force also acts on a current-carrying
wire? Depend your answer.
Yes, simple logic tells you that if a charged particle moving through a
magnetic field experiences a deflecting force, then a current of charged
particles moving through a magnetic field also experiences a deflecting
force.
17. What relative direction between a magnetic field and a currentcarrying wire results in the greatest force on the wire? In the
smallest force?
The force is strongest when the current is perpendicular to the magnetic
fields lines. Smallest force is the weakest.
18. What happens to the direction of the magnetic force on a wire in
a magnetic field when the current in the wire is reversed?
If we reverse the direction of current, the deflecting force acts in the opposite
direction. The force is strongest when the current is perpendicular to the
magnetic field lines.
19. What is a galvanometer called when it is calibrated to read
current? To read voltage?
When galvanometer calibrated to read current is an Ammeter, to read
voltage is a voltmeter.
Exercises – page 242
1. Since every iron atom is a tiny magnet, why aren’t all iron
materials themselves magnets?
All iron materials are not magnetized because the tiny magnetic domains are
most often oriented in random directions and cancel one another's effects.
3.What is different about the magnetic poles of common refrigerator
magnets compared with those of common bar magnets?
Refrigerator magnets have narrow strips of alternating north and south
poles. These magnets are strong enough to hold sheets of paper against a
refrigerator door, but have a very short range because the north and south
poles cancel a short distance from the magnetic surface.
5. “An electron always experiences a force in an electric field, but
not always in magnetic field.” Defend this statement.
An electron always has its own electric field around it but only has a
magnetic field when it is moving.
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8. One way to make a compass is to stick a magnetized needle into a
piece of cork and to float it in a glass bowl full of water. The needle
will align itself with the horizontal component of Earth’s magnetic
field. Since the north pole of this compass is attracted northward,
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will the needle float toward the north side of the bowl? Defend your
answer.
No the needle will remain at rest. The magnetic field of earth will exert equal
and opposite forces on the two poles of the needle. The forces will balance
each other, keeping the needle at rest.
13. Magnet A has twice the magnetic field strength of magnet B,
and, at a certain distance, it pulls on magnet B with a force of 50 N.
With how much force, then, does magnet B pull on magnet A?
50 N Newton’s 3rd law
14. In Figure 11.17, we see a magnet exerting a force on a currentcarrying wire. Does a current-carrying wire exert a force on a
magnet? Why or why not?
With current flowing in the wire, the magnet pushes the wire away from the magnet
because a force is exerted on a moving charge (or current) in a wire moving
perpendicular to a magnetic field. A magnetic field exerts a force on a currentcarrying wire. The direction of that force depends on the direction of current flow
and the orientation of the magnetic field according to the right-hand rule.
17. Can an electron at rest in a magnetic field be set into motion by
the magnetic field? What if it were at rest in an electric field?
No
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