Unit 8.3 Quiz 5

Which choice of core material for a solenoid (coiled wire) will result in the strongest electromagnetic field if all other factors remain equal?

• titanium

• plastic

• aluminum

• iron

Answer explanation

Iron is a ferromagnetic material, which means it can be magnetized and significantly enhances the magnetic field produced by a solenoid. This makes it the best choice for achieving the strongest electromagnetic field.

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Which of the following would be the best electromagnet if the same amount of current was sent through each?

• Coil of wire with 20 turns wrapped around a cardboard core.

• Coil of wire with 50 turns wrapped around a cardboard core.

• Coil of wire with 20 turns wrapped around an iron core.

• Coil of wire with 50 turns wrapped around an iron core.

Answer explanation

The best electromagnet is the coil with 50 turns around an iron core. More turns increase the magnetic field strength, and the iron core enhances this effect, making it the most effective option.

Which of the following compasses represents the magnetic field at point X?

• A

• B

• D

• E

• F

Answer explanation

Compass F correctly shows the direction of the magnetic field at point X, aligning with the magnetic north and indicating the field's orientation accurately.

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Earth’s magnetic field is most likely due to:

• the rotation of Earth acting on all of Earth's magnetite.

• convection currents in the molten parts of Earth’s interior.

• a magnetized solid inner core of the Earth.

• the high concentration below the Earth’s surface of lodestone, a natural magnet.

• millions of small magnets buried in the Earth.

Answer explanation

Earth's magnetic field is primarily generated by convection currents in the molten outer core, which create electric currents and, consequently, a magnetic field. This process is more significant than the other options.

Suppose you move the left magnet closer to the right magnet as shown. What will happen as the magnets are moved closer together?

• The magnets will not interact until they touch each other.

• At some point, the two magnets will begin to attract each other.

• Since a person is pushing the magnet forward, it is the person applying the force, not the magnet.

• The force between the magnets will not change.

• The force between the magnets will increase as they get closer together.

Answer explanation

As the magnets are moved closer together, the magnetic force between them increases due to the nature of magnetic fields. This means that the correct choice is that the force between the magnets will increase as they get closer together.

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The magnetic field strength of a magnet is strongest:

• at both poles.

• at the north pole.

• at the south pole.

• all around the surface.

• in the middle.

Answer explanation

The magnetic field strength of a magnet is strongest at both poles because these areas have the highest concentration of magnetic field lines, making them the most powerful points of the magnet.

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If you put a small compass in a magnetic field, the compass will:

• seek electrical charge concentrations.

• repel the field lines with the same charge.

• swing or rotate randomly.

• line up in a direction parallel to the magnetic field lines.

• line up in a direction perpendicular to the magnetic field lines.

Answer explanation

A small compass contains a magnetized needle that aligns itself with the magnetic field. Therefore, it will line up in a direction parallel to the magnetic field lines, indicating the direction of the magnetic field.

A magnet can attract an unmagnetized paperclip because:

• paperclips become permanently magnetized in a magnetic field.

• a magnet can attract any metal.

• paperclips become temporarily magnetized in a magnetic field.

• a magnet exerts a force on any object.

• paperclips are really magnetized.

Answer explanation

A magnet can attract an unmagnetized paperclip because it temporarily magnetizes the paperclip, aligning its domains to create a magnetic field that allows attraction.

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