Unit 04.12: Magnetism and Induction

Where is the magnitude of the magnetic field around a permanent magnet greatest?

close to the poles

Which compass needle orientation in the figure above might correctly describe the magnet’s field at that point?

A

Which describes magnetic declination

the angle between directions to true north and magnetic

The current in a long wire creates a magnetic field in the region around the wire. How is the strength of that field at a given distance, r, from the wire's center related to r?

the field is inversely proportional to r

A current in a solenoid coil creates a magnetic field inside the coil. The field strength is directly proportional to the

current

A current in a solenoid with N turns creates a magnetic field inside the solenoid. The magnetic field strength is directly proportional to the

number of turns in the loop and the strength of the current.

A current in a long, straight wire produces a magnetic field. These magnetic field lines

from circles that go around the wire.

If a wire is carrying a strong, steady current, the magnetic field is

proportional to the current and inversely proportional to the distance from the wire.

Which orientation characterizes the magnetic domains in a nonmagnetized piece of iron?

random

In a permanent magnet,

domain alignment persists after the external magnetic field is removed.

When an iron rod is inserted into a solenoid coil's center, the magnetic field produced by the current in the loops

causes alignment of the domains in the iron.

The direction of the force on a current-carrying wire in an external magnetic field is

perpendicular to the current and to the magnetic field

What is the path of an electron moving perpendicular to a uniform magnetic field?

a circle

What is the path of an electron moving parallel to a uniform magnetic field?

straight line

A stationary positive charge, Q, is located in a magnetic field, B, which is directed toward the right, as shown in the figure above. The direction of the magnetic force on Q is

There is no magnetic force.

Consider two long, straight, parallel wires, each carrying a current I. If the currents move in opposite directions,

the two wires will repel each other.

Consider two long, straight, parallel wires, each carrying a current I. If the currents move in the same direction,

the two wires will attract each other.

A current-carrying conductor in and perpendicular to a magnetic field experiences a force that is

perpendicular to the current.

A loop wire is held in a vertical position at the equator with the face of the loop facing in the east-west direction. What change will induce the greatest current in the loop.

rotating the loop so its face is north-south

A bar magnet falls through a loop of wire with constant velocity, and the north pole enters the loop first. The induced current will be greatest when the magnet is located so that the loop is

near either the north or the south pole.

Electricity may be generated by rotating a loop of wire between the poles of a magnet. The induced current is greatest when

the plane of the loop is perpendicular to the magnetic field.

According to Lenz’s law, the magnetic field of an induced current in a conductor will

oppose a change in the applied magnetic field.

According to Lenz’s law, if the applied magnetic field changes.

the induced field attempts to keep the total field strength constant.

The operation of an electric motor depends on

the force acting on a current-carrying wire in a magnetic field.

Which conversion process is the basic function of the electric generator?

mechanical energy to electrical energy

Which conversion process is the basic function of the electric motor?

electrical energy to mechanical energy

Under which condition is the back emf in an electric motor at its maximum value?

motor speed is at maximum

In most electric generators, either the armature or the magnetic field is ____, generating a(n) ____.

rotated; induced current

In a primary-secondary coil combination, the current in the secondary is maximum at the moment that which condition is met in the primary?

the rate of current change is maximum

In a two-coil system, the mutual inductance depends on

both the geometrical properties of the coils and their orientation to each other.

The self-inductance of a solenoid increases under which condition?

number of coils is increased

How is the emf in a current-carrying inductor related to its self-inductance, L?

It is directly proportional to L.

How is the energy stored in a current-carrying inductor related to the current value, I?

It is directly proportional to DI.

By what factor is the self-induction of a coil changed if its number of coil turns is tripled?

3

The source of a material's magnetism is the:

spin of its electrons.

If a 6-inch long bar magnet is cut one inch from the north pole end of the magnet:

both pieces have a north and a south pole on each end.

Mike and Tom are trying to make a permanent magnet by stroking different metal bars with a owerful magnet. Which of the four metals is the poorest choice for their permanent magnet?

Copper

The magnitude of the magnetic field around a permanent magnet:

is greatest close to the poles.

The force between two bar magnets is measured as the magnets are moved away from one another. Which graph below best represents the relationship between the magnetic force and the distance between the magnets?

D

Which pair of objects in the diagram below experiences a repulsive force?

B

Which compass in the diagram below is pointing in the wrong direction?

D

A magnet is shown surrounded by its magnetic field. In which area is themagnetic field strongest?

D

Materials containing equal numbers of electrons with opposing spins are called:

ferromagnetic

Concerning the electron and magnetism, all of the following statements are true EXCEPT:

electrons spin on their axes similar to the way the Earth spins on its axis.

All of the following can be permanently strongly magnetized EXCEPT

tungsten steel

The direction of the magnetic field near the center of the current-carrying loop in the diagram is:

into the page.

The diagram shows a coil of wire connected to a battery. The north pole of this coil is closest to:

C

Electromagnets are generally more useful than permanent magnets for all of the following reasons EXCEPT:

they are always magnetized.

An electric current moving upward through a straight conductor creates a magnetic field. The diagram that correctly represents this magnetic field is:

C

The device that switches the polarity of the electromagnets giving motion to the rotar in an electric motor is the:

commutator

The rotating element of a motor is often referred to as the:

armature.

The key components of a motor include all of the following EXCEPT a:

double-throw knife switch.

the device that uses electromagnetic induction to produce electricity is called a:

generator.

When a magnet moves into a coil of wire, electric current is caused to flow by:

induction.

The rotating machines driven by the flow of heated air that cause electrical generators to turn are called:

turbines.

Electricity can be generated if a loop of wire is turned between the poles of a magnet. The induced current will be greatest when the:

plane of the loop is parallel to the magnetic field.

A current can be induced to flow in a coil in all of the following situations EXCEPT:

holding a powerful magnet in the middle of a coil of wire.

A generator's basic function is to convert:

mechanical energy to electrical energy.

A motor's basic function is to convert:

electrical energy to mechanical energy.

The motion of a magnet that induces the greatest alternating current to flow in a coil is:

rapid back and forth movement of the magnet in the coil.