Question 1

A typical bar magnet has an "N" stamped on its north pole end and an "S"
Stamped on its south pole end. With the right tools, you might be able to change this bar magnet in one or more of the following ways: (1) remove its magnetic poles altogether, (2) reverse its magnetic poles so that it has a north pole at the end stamped "S"
And a south pole at the end stamped "N", (3) convert its north pole into a south pole so that it has south poles at both ends and no north poles. Which of those three options is physically possible?
A) Only (1) and (2)
B) None of them is possible.
C) Only (2) and (3)
D) All three are possible.

Accepted Answer

Magnetic poles always come in pairs. You cannot remove one pole without removing the other.

Question 2

Why can't you float one permanent magnet directly above another permanent magnet indefinitely by turning their north poles toward one another?
A) Two north poles attract one another and the two magnets will pull together until they touch.
B) That arrangement is unstable-the upper magnet will fall to the side or flip over.
C) The repulsive forces between magnets cannot overcome the gravitational forces between them, so the upper magnet cannot float.
D) Because they are stationary, the two magnets exert no forces on one another and the top magnet falls.

Accepted Answer

The arrangement of two magnets with like poles facing each other creates an unstable equilibrium. If the upper magnet is slightly displaced, it will experience a torque that causes it to flip over or move to the side rather than maintaining its position floating above the other magnet.

Question 3

You are working with a magnet and it breaks in half. You then end up with
A) One north and one south pole
B) Two south poles only
C) Two north poles only
D) Two magnets, each with a south and a north pole.

Accepted Answer

When a magnet is broken in half, each half becomes a separate magnet, with its own north and south pole. Magnets always have both a north and south pole, regardless of how many times they are divided.

Question 4

Which of the following is not ferromagnetic?
A) Iron
B) Nickel
C) Aluminum
D) Chromium dioxide

Accepted Answer

Aluminum is not ferromagnetic. Iron, Nickel, and Chromium dioxide are all examples of ferromagnetic materials, which means they can be magnetized or attracted to a magnet. Aluminum, on the other hand, is paramagnetic, which means it does not retain magnetic properties when the external magnetic field is removed.

Question 5

Which is not a characteristic of hard magnetic materials?
A) They are hard to magnetize.
B) They easily lose their magnetization.
C) They are used in magnetic tapes.
D) They have microscopic structures and defects that impede the resizing of domains.

Accepted Answer

Hard magnetic materials do not easily lose their magnetization; this is a characteristic of soft magnetic materials. Hard magnetic materials retain their magnetization and are used in applications where a permanent magnet is required.

Question 6

A magnet factory is making bar magnets, each about the size and shape of an ordinary ruler. After forming each bar of metal, that bar must be magnetized. The bar is placed in a coil of wire and a huge pulse of current is sent through the coil. During the pulse, current is only sent in one direction through the coil: a pulse of direct current or DC. If, instead, the current reversed directions rapidly during the pulse-a pulse of alternating current or AC-then
A) the bar magnet would end up with two south poles and no north poles.
B) the poles of the bar magnet would also reverse rapidly and would end up with a magnetization that depends upon what the AC current was at the precise moment it was shut off.
C) the bar would become overmagnetized because AC is much more magnetic than DC.
D) the bar magnet would end up with two north poles and no south poles.

Accepted Answer

Using alternating current (AC) to magnetize a bar would cause the magnetic field direction in the bar to change direction rapidly, following the changes in the current's direction. The final magnetization of the bar would depend on the magnetic field direction at the moment the current is turned off, not resulting in a bar with two south or two north poles, nor in overmagnetization due to AC being "more magnetic" than DC.

Question 7

The north pole of a permanent magnet is clinging to the front surface of your steel refrigerator, so the refrigerator clearly has a south pole at its surface. If you flip the permanent magnet over, so that its south pole faces the refrigerator, the refrigerator will
A) keep a south pole at its surface and attract the permanent magnet.
B) place a north pole at its surface and attract the permanent magnet.
C) place a north pole at its surface and repel the permanent magnet.
D) keep a south pole at its surface and repel the permanent magnet.

Accepted Answer

When a magnet is brought close to a ferromagnetic material like steel, the material temporarily acts as a magnet itself. The side facing the magnet's north pole becomes a south pole to attract it, and if flipped, the material's side facing the magnet's south pole becomes a north pole, again to attract it.

Question 8

Suppose you have a machine which has a very strong magnet inside. You have some computer disks in the room and, although you think they are far away enough from the magnet to be safe, you don't want to take any risks. What material would be appropriate for building a magnetic shielding enclosure?
A) aluminum.
B) plastic.
C) iron.
D) copper.

Accepted Answer

Iron is an appropriate material for building a magnetic shielding enclosure because it has high magnetic permeability, which allows it to absorb and redirect magnetic fields away from the protected area, effectively shielding any items inside the enclosure from the external magnetic field.

Question 9

You are working on an experiment involving a very strong permanent magnet, and your data suggests that your magnet's field suddenly decreased during some interval in time. Such a decrease could have been caused by the magnet
A) having overheated substantially.
B) being hit hard.
C) both (A) and (B).
D) being grounded out.

Accepted Answer

Permanent magnets can lose their magnetism if they are heated above their Curie temperature or if they are subjected to a physical shock, such as being hit hard. Both overheating and physical impact can disrupt the alignment of the magnetic domains within the magnet, leading to a decrease in its magnetic field.

Question 10

Two permanent magnets
A) always attract.
B) can attract or repel.
C) always repel.
D) never have stable force interactions.

Accepted Answer

Permanent magnets can either attract or repel each other depending on the orientation of their poles. Opposite poles attract, while like poles repel.

Question 11

A steel refrigerator door is not permanently magnetic because
A) All the magnetic domains are oriented randomly
B) There are no magnetic domains
C) The electrons are bound and can't move around much
D) The door is usually ground out and loses all its magnetism.

Accepted Answer

Steel refrigerator doors are not permanently magnetic because the magnetic domains within them are oriented randomly. This random orientation means that the magnetic fields of the individual domains cancel each other out, resulting in no overall magnetic field.

Question 12

Electricity and magnetism are different because
A) There are no electric monopoles.
B) There are no magnetic monopoles.
C) Electrical forces decrease with increasing separation.
D) Only magnetism has to do with electrons.

Accepted Answer

Magnetic monopoles do not exist according to current scientific understanding, whereas electric charges exist as both positive and negative (monopoles). This is a fundamental difference between electricity and magnetism.

Question 13

A permanent magnet and a magnetizable material like steel Two permanent magnets
A) always attract.
B) can attract or repel.
C) always repel.
D) never have stable force interactions.

Accepted Answer

The answer of A permanent magnet and a magnetizable material...

Question 14

You are working in a laboratory over the summer and you measure the magnetic field in a coil to be 3T. You insert a steel rod which has a pole strength 500 A-m. The amount of force on the rod is
A) 0
B) 3 N
C) 1500 N
D) 1500 N-m

Accepted Answer

The force on a magnetic dipole (such as a steel rod with a given pole strength) in a uniform magnetic field is given by the equation $F = pB$, where $p$ is the pole strength of the magnet and $B$ is the magnetic field strength. Here, $p = 500 \, \text{A-m}$ and $B = 3 \, \text{T}$, so the force $F = 500 \times 3 = 1500 \, \text{N}$.

Question 15

You are working in a laboratory over the summer and you measure the magnetic field in a coil to be 2T. You insert a steel rod which has a pole strength 5 A-m outside the magnet. The amount of force on the rod
A) is 0
B) is 2 N
C) is 1000 N
D) cannot be determined because the pole strength of the steel will change inside the magnet.

Accepted Answer

The answer of You are working in a laboratory over...

Question 16

Although you would like for your date to have a magnetic personality, the field of magnetic dating is about something else altogether. The idea is that magnetic rocks get very hot in or near a fire and then when they cool down they take on the magnetic field of the earth at whatever time they cooled. The reason heat is needed is because
A) There needs to be enough thermal fluctuations to disorient the magnetic domains and cause the rock to be non - magnetic.
B) There needs to be enough thermal fluctuations to disorient the magnetic domains and cause the rock to be magnetic.
C) The fire causes a chemical reaction on the surface of the rock that preserves magnetic field direction.
D) Fire is just dramatic.

Accepted Answer

When rocks are heated, the thermal energy causes the magnetic domains to become disoriented, making the rock temporarily non-magnetic. Upon cooling, the domains realign with the Earth's magnetic field, preserving its direction at that time.

Question 17

When you drop a strong magnet through the center of a copper pipe, the magnet
A) descends slowly because it is attracted to the magnetic copper metal.
B) descends rapidly because its motion causes currents to flow in the pipe and those currents attract the magnet.
C) falls at the usual rate because copper metal is nonmagnetic.
D) descends slowly because its motion causes currents to flow in the pipe and those currents repel the magnet.

Accepted Answer

The magnet descends slowly through the copper pipe due to Lenz's Law, which states that the induced currents (eddy currents) in the copper pipe will create magnetic fields that oppose the magnet's motion, effectively slowing its descent. Copper is not magnetic, but it is a good conductor, so the magnet's motion induces these currents.

Question 18

If you float an aluminum pie plate on the surface of a pond and move the north pole of a strong magnet in a clockwise circle just above that plate, the plate will
A) begin turning counter-clockwise, as though it were being twisted away from the magnet.
B) begin turning clockwise, as though it were being dragged along with the magnet.
C) remain stationary.
D) be lifted out of the water and will stick to the strong north pole above it.

Accepted Answer

The aluminum pie plate will begin turning clockwise, following the motion of the magnet. This occurs due to electromagnetic induction, where the moving magnetic field induces eddy currents in the conductive aluminum plate. These currents create their own magnetic field, which interacts with the original magnetic field of the magnet, causing the plate to move in the direction of the magnet's movement.

Question 19

When you drop the north pole of a permanent magnet onto an aluminum sheet, it falls slightly slower than normal. The magnet is being repelled by the aluminum because
A) aluminum is positively charged and repels approaching magnetic poles.
B) aluminum has a net north magnetic pole that repels any approaching north poles.
C) aluminum has a net south magnetic pole that repels any approaching north poles.
D) current induced in the aluminum by the approaching north pole produces a repelling north pole on the aluminum's surface.

Accepted Answer

When a magnet moves towards a conductor like aluminum, it induces electric currents (known as eddy currents) in the conductor. According to Lenz's law, these currents create their own magnetic field which opposes the change that caused them. In this case, the induced magnetic field in the aluminum acts to repel the approaching north pole of the magnet, slowing its fall. This is a manifestation of electromagnetic induction, not a result of permanent magnetic properties or static electric charges in the aluminum.

Question 20

If you move the north pole of a permanent magnet toward the surface of an aluminum pot, a current will flow through that pot and the pot will become magnetic-repelling your permanent magnet. If you stop the permanent magnet just before it touches the pot and then hold the permanent magnet stationary, the repulsive force between the pot and the permanent magnet will gradually disappear. The repulsive force disappears because the electric current in the pot
A) becomes non-magnetic once the permanent magnet stops moving.
B) stops increasing and becomes steady once the permanent magnet stops moving.
C) gradually slows to a stop once the permanent magnet stops moving.
D) becomes an alternating current once the permanent magnet stops moving and the pot's magnetic poles then flip back and forth rapidly.

Accepted Answer

The repulsive force disappears because the electric current in the pot, which is induced by the movement of the magnet, gradually slows to a stop once the permanent magnet stops moving. This is due to Lenz's law, which states that the direction of the induced current will be such that it opposes the change in magnetic flux that produced it. When the magnet stops moving, there's no change in magnetic flux to maintain the induced current, so the current and the resulting magnetic field it creates gradually disappear.

Quiz 11: Magnetism and Electrodynamics

Why can't you float one permanent magnet directly above another permanent magnet indefinitely by turning their north poles toward one another?

You are working with a magnet and it breaks in half. You then end up with

Which of the following is not ferromagnetic?

Which is not a characteristic of hard magnetic materials?

The north pole of a permanent magnet is clinging to the front surface of your steel refrigerator, so the refrigerator clearly has a south pole at its surface. If you flip the permanent magnet over, so that its south pole faces the refrigerator, the refrigerator will

Suppose you have a machine which has a very strong magnet inside. You have some computer disks in the room and, although you think they are far away enough from the magnet to be safe, you don't want to take any risks. What material would be appropriate for building a magnetic shielding enclosure?

You are working on an experiment involving a very strong permanent magnet, and your data suggests that your magnet's field suddenly decreased during some interval in time. Such a decrease could have been caused by the magnet

Two permanent magnets

A steel refrigerator door is not permanently magnetic because

Electricity and magnetism are different because

A permanent magnet and a magnetizable material like steel Two permanent magnets

You are working in a laboratory over the summer and you measure the magnetic field in a coil to be 3T. You insert a steel rod which has a pole strength 500 A-m. The amount of force on the rod is

You are working in a laboratory over the summer and you measure the magnetic field in a coil to be 2T. You insert a steel rod which has a pole strength 5 A-m outside the magnet. The amount of force on the rod

When you drop a strong magnet through the center of a copper pipe, the magnet

If you float an aluminum pie plate on the surface of a pond and move the north pole of a strong magnet in a clockwise circle just above that plate, the plate will

When you drop the north pole of a permanent magnet onto an aluminum sheet, it falls slightly slower than normal. The magnet is being repelled by the aluminum because