Chapter 24

Magnetism

For magnets, like poles repel each other and unlike poles

a. also repel each other.

b. attract each other.

c. can disappear into nothingness.

d. can carry a lot of energy.

For magnets, like poles repel each other and unlike poles

a. also repel each other.

b. attract each other.

c. can disappear into nothingness.

d. can carry a lot of energy.

The source of all magnetism is

a. tiny bits of iron.

b. tiny domains of aligned atoms.

c. the motion of electrons.

d. small lodestones.

The source of all magnetism is

a. tiny bits of iron.

b. tiny domains of aligned atoms.

c. the motion of electrons.

d. small lodestones.

Comment: This is true for electrons moving in a beam or electrons spinning or orbiting the nuclei of atoms such as iron.

A strong magnet lifts a paper clip. Compared with the force the magnet exerts on the clip, the force the clip

exerts on the magnet is

a. much less.

b. slightly less.

c. the same.

d. slightly more.

A strong magnet lifts a paper clip. Compared with the force the magnet exerts on the clip, the force the clip

exerts on the magnet is

a. much less.

b. slightly less.

c. the same.

d. slightly more.

Explanation: This is Newton’s third law. In the interaction between the paper clip and the magnet, both forces are equal and opposite.

Magnet A has twice the field strength of Magnet B. When brought close

together, the magnet that pulls harder on the other is

a. Magnet A.

b. Magnet B.

c. Both forces are equally strong.

d. dependent on their distances apart.

Magnet A has twice the field strength of Magnet B. When brought close

together, the magnet that pulls harder on the other is

a. Magnet A.

b. Magnet B.

c. Both forces are equally strong.

d. dependent on their distances apart.

Explanation: This is Newton’s third law–the force that A exerts on B is equal and opposite to the force that B exerts on A.

Surrounding moving electric charges are

a. electric fields.

b. magnetic fields.

c. Both of these.

d. None of these.

Surrounding moving electric charges are

a. electric fields.

b. magnetic fields.

c. Both of these.

d. None of these.

Comment: Don’t forget that electric fields surround electric charges!

The magnetic domains in a magnet produce a weaker magnet when the

magnet is

a. heated.

b. dropped on a hard surface.

c. Either of these.

d. None of these.

The magnetic domains in a magnet produce a weaker magnet when the

magnet is

a. heated.

b. dropped on a hard surface.

c. Either of these.

d. None of these.

Magnetic domains occur mainly for materials composed of

a. carbon.

b. copper.

c. silver.

d. iron.

Magnetic domains occur mainly for materials composed of

a. carbon.

b. copper.

c. silver.

d. iron.

A bar magnet that holds a chain of paper clips illustrates

a. magnetic field displacement.

b. magnetic induction.

c. electromagnetic induction.

d. Faraday’s law.

A bar magnet that holds a chain of paper clips illustrates

a. magnetic field displacement.

b. magnetic induction.

c. electromagnetic induction.

d. Faraday’s law.

When a bar magnet is broken in half, the magnetic strength of each piece is

a. less than half.

b. about half.

c. the same.

d. somewhat increased.

When a bar magnet is broken in half, the magnetic strength of each piece is

a. less than half.

b. about half.

c. the same.

d. somewhat increased.

Explanation: This is detailed in Figure 24.7 in the textbook.

A superconducting electromagnet makes use of

a. low-resistance coils of wire.

b. super-high temperatures.

c. high-speed electrons.

d. close packing of high-density magnetic domains.

A superconducting electromagnet makes use of

a. low-resistance coils of wire.

b. super-high temperatures.

c. high-speed electrons.

d. close packing of high-density magnetic domains.

The magnetic field lines about a current-carrying wire form

a. circles.

b. radial lines.

c. eddy currents.

d. spirals.

The magnetic field lines about a current-carrying wire form

a. circles.

b. radial lines.

c. eddy currents.

d. spirals.

A magnetic force cannot act on an electron when it

a. is at rest.

b. moves parallel to magnetic field lines.

c. Both of these.

d. None of these.

A magnetic force cannot act on an electron when it

a. is at rest.

b. moves parallel to magnetic field lines.

c. Both of these.

d. None of these.

Explanation: A force is exerted on charged particles only when they move at an angle to magnetic field lines. The force is greatest when motion is at right angles to the magnetic field.

A magnetic force acts most strongly on a current-carrying wire when it

a. carries a very large current.

b. is perpendicular to the magnetic field.

c. Either or both of these.

d. None of the above.

A magnetic force acts most strongly on a current-carrying wire when it

a. carries a very large current.

b. is perpendicular to the magnetic field.

c. Either or both of these.

d. None of the above.

The fact that a force is exerted on a current-carrying wire in a magnetic

field underlies

a. motors.

b. electric meters.

c. Both of these.

d. None of these.

The fact that a force is exerted on a current-carrying wire in a magnetic

field underlies

a. motors.

b. electric meters.

c. Both of these.

d. None of these.

An electric meter operates on the principal that a current-carrying wire

or coil will

a. interact with a magnetic field.

b. deflect away from a magnetic field.

c. be attracted to a magnet.

d. induce a magnetic field when near a magnet.

An electric meter operates on the principal that a current-carrying wire

or coil will

a. interact with a magnetic field.

b. deflect away from a magnetic field.

c. be attracted to a magnet.

d. induce a magnetic field when near a magnet.

Surrounding our Planet Earth are

a. radiation belts.

b. cosmic rays.

c. gravitational and magnetic fields.

d. All of these.

Surrounding our Planet Earth are

a. radiation belts.

b. cosmic rays.

c. gravitational and magnetic fields.

d. All of these.

A magnetic force acting on a beam of electrons can change

a. only the direction of the beam.

b. only the energy of the electrons.

c. both the direction and the energy.

d. neither the direction nor the energy.

A magnetic force acting on a beam of electrons can change

a. only the direction of the beam.

b. only the energy of the electrons.

c. both the direction and the energy.

d. neither the direction nor the energy.

The magnetic field surrounding Earth

a. helps shield us from cosmic rays.

b. is likely caused by electric currents in its interior.

c. changes over time.

d. All of these.

The magnetic field surrounding Earth

a. helps shield us from cosmic rays.

b. is likely caused by electric currents in its interior.

c. changes over time.

d. All of these.

Earth’s magnetic poles and geographical poles occur

a. atop each other.

b. about 1000 miles apart.

c. in northern Canada.

d. beneath ice caps.

Earth’s magnetic poles and geographical poles occur

a. atop each other.

b. about 1000 miles apart.

c. in northern Canada.

d. beneath ice caps.

Magnetic materials are found in the bodies of

a. bees.

b. birds.

c. bacteria.

d. All of these.

Magnetic materials are found in the bodies of

a. bees.

b. birds.

c. bacteria.

d. All of these.