Deck 25: Electromagnetic Induction

Question 1

Voltage can be induced in a wire by

A)moving the wire near a magnet.
B)moving a magnet near the wire.
C)changing the current in a nearby wire.
D)all of the above
E)none of the above

Answer 1

all of the above

Question 2

The amount of current produced by electromagnetic induction depends on the

A)amount of induced voltage.
B)resistance of the circuit to which it is connected.
C)both of these
D)neither of these

Answer 2

both of these

Question 3

Faraday's law underlies the operation of

A)an electric guitar.
B)a shake flashlight.
C)the changing of traffic lights.
D)all of the above
E)none of the above

Answer 3

all of the above

Question 4

The metal detectors that people walk through at airports operate via

A)Ohm's law.
B)Faraday's law.
C)Coulomb's law.
D)Newton's laws.
E)civil laws.

Question 5

The frequency of induced voltage in a wire coil depends on

A)the frequency of current producing it.
B)how frequently a magnet dips in and out of the coil.
C)the number of loops in the coil.

Question 6

Electromagnetism unites

A)electricity and magnetism.
B)electric and gravitational fields.
C)physics and biophysics.
D)all of the above
E)none of the above

Question 7

When voltage is induced in a coil of wire, current is

A)also induced.
B)not induced.
C)cancelled.

Question 8

A device that transforms electrical energy to mechanical energy is a

A)generator.
B)motor.
C)transformer.
D)magnet.
E)none of the above

Question 9

Electromagnetic induction is employed in

A)electric power lines.
B)triggering traffic lights.
C)hybrid automobiles.
D)mobile phones.
E)all the above

Question 10

When a change occurs in the magnetic field in a closed loop of wire

A)a voltage is induced in the wire.
B)a current is created in the loop of wire.
C)electromagnetic induction occurs.
D)all of the above
E)none of the above

Question 11

Fred swings a sheet of copper in pendulum fashion between the poles of a strong magnet. The sheet slows in entering the magnetic field because it

A)induces swirling currents in the copper and accompanying magnetic fields that resist motion.
B)experiences both air and magnetic friction.
C)is repelled by free electrons in the copper.
D)none of the above

Question 12

Thrust a magnet into the opening of a rubber band and it

A)rotates.
B)then has a current in it.
C)both of these
D)neither of these

Question 13

When a bar magnet is thrust into a coil of copper wire, the coil tends to

A)attract the magnet as it enters.
B)repel the magnet as it enters.
C)both of these
D)neither of these

Question 14

Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is

A)of low wattage.
B)of high wattage.
C)turned off.
D)none of the above

Question 15

Electromagnetic induction occurs in a coil when there is a change in

A)electric field intensity in the coil.
B)magnetic field intensity in the coil.
C)electromagnetic polarity.
D)none of the above

Question 16

If you thrust a magnet into a closed loop of wire, the loop will

A)rotate.
B)have a current in it.
C)both of these
D)neither of these

Question 17

Magnetic field strength inside a current-carrying coil will be greater if the coil encloses a

A)vacuum.
B)wooden rod.
C)glass rod.
D)rod of iron.
E)none of the above

Question 18

When a magnet is moved to and fro in a wire coil, voltage is induced. If the coil has twice as many loops, the voltage induced is

A)half.
B)the same.
C)twice.
D)four times as much.
E)none of the above

Question 19

If you drop a bar magnet in a vertical copper pipe it will fall slowly because

A)of air resistance.
B)it induces a magnetic field in the pipe that resists motion of the magnet.
C)the copper is a good conductor of both electricity and magnetism.
D)of electron repulsion.

Question 20

The discovery of electromagnetic induction is credited to

A)Joseph Henry in America.
B)Michael Faraday in England.
C)both of these
D)neither of these

Question 21

If the voltage produced by a generator alternates, it does so because

A)unlike a battery, it produces alternating current.
B)the changing magnetic field that produces it alternates.
C)of alterations in the mechanical energy input.
D)all of the above
E)none of the above

Question 22

Compared to the primary voltage, the secondary voltage can be

A)higher.
B)lower.
C)the same.
D)any of the above
E)none of the above

Question 23

The major advantage of MHD generators over conventional generators is that MHD generators

A)do not use electromagnetic induction.
B)do not require magnets.
C)require no power input.
D)all of the above
E)none of the above

Question 24

Transformers use ac to satisfy the required

A)transfer of energy from coil to coil.
B)voltage for transformation.
C)change in magnetic field for operation.
D)change in input current.
E)magnetic field intensities.

Question 25

The rate at which energy is transferred is

A)power.
B)electromagnetic induction.
C)transformation.
D)none of the above

Question 26

An efficient step-down transformer decreases

A)power.
B)energy.
C)both of these
D)neither of these

Question 27

A transformer transforms voltage while

A)producing energy.
B)producing power.
C)transferring energy from one coil to another.
D)transferring current from one coil to another.

Question 28

A device that transforms mechanical energy into electrical energy is a

A)generator.
B)motor.
C)transformer.
D)magnet.
E)none of the above

Question 29

An electric motor is very similar to

A)an electric generator.
B)an automobile battery.
C)a radio receiver.
D)none of the above

Question 30

The current produced by a common generator is

A)dc.
B)ac.
C)neither of these

Question 31

A transformer actually transforms

A)voltage.
B)magnetic field lines.
C)generators into motors.
D)non-safe forms of energy to safe forms of energy.
E)all of the above

Question 32

The output power of an ideal transformer is

A)greater than the input power.
B)equal to the input power.
C)smaller than the input power.
D)may be any of the above

Question 33

The primary of a transformer is the coil connected to

A)the load.
B)the Internet.
C)the input power line.
D)none of the above

Question 34

The principle difference between a step-up and step-down transformer is

A)step-up transformers can handle more current.
B)different geometries.
C)different ratios of turns of wire for each.
D)none of the above

Question 35

A transformer produces

A)energy.
B)power.
C)neither, but transforms mechanical energy to electric energy.
D)none of the above

Question 36

A principle difference between an MHD generator and a conventional generator is that the MHD generator

A)has no moving parts.
B)operates more efficiently at high temperatures.
C)both of these
D)neither of these

Question 37

The secondary of a transformer is the coil connected to

A)the load.
B)the Internet.
C)the input power line.
D)none of the above

Question 38

An efficient step-up transformer boosts

A)energy.
B)power.
C)voltage.
D)all of the above
E)none of the above

Question 39

A generator armature is more difficult to rotate when supplying electric current due to

A)an induced magnetic field in the windings that resists change.
B)increased resistance.
C)energy leaking as heat.
D)none of the above

Question 40

A turbogenerator produces

A)energy.
B)power.
C)neither, but transforms energy from one form to another.
D)none of the above

Question 41

A certain transformer doubles input voltage. If the primary coil draws 10 A of current, then the current in the secondary coil is

A)2 A.
B)5 A.
C)10 A.
D)25 A.
E)none of the above

Question 42

If the primary of a transformer is connected to a dc power source, the transformer would have a voltage output

A)at a higher efficiency than with an ac source.
B)the same.
C)that is also dc.
D)only while being connected or disconnected.
E)none of the above

Question 43

Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage may be produced by

A)the sudden collapse in the magnetic field.
B)latent energy in the battery.
C)the resistance of the battery to a change in polarity.
D)electrons already in the wire.
E)the electric field between the battery terminals.

Question 44

A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is

A)60 V.
B)120 V.
C)1200 V.
D)12000 V.
E)none of the above

Question 45

Between the consumer and the power plant, most importantly, are

A)huge capacitors.
B)generators.
C)step-down transformers.
D)all of the above
E)none of the above

Question 46

The voltage induced in self-inductions is

A)always in a direction opposing the changing voltage that produced it.
B)likely higher than the changing voltage that causes it.
C)both of these
D)neither of these

Question 47

Power is transmitted at high voltages because the corresponding current in the wires is

A)also high to deliver appreciable power to distant places.
B)low so that overheating of the wires is minimized.
C)either of these
D)neither of these

Question 48

The principal advantage of ac power over dc power is that

A)more energy is dissipated during transmission.
B)ac voltage oscillates while dc voltage does not.
C)ac voltage can be transformed via conventional transformers.
D)ac circuits multiply power more easily.
E)ac circuits are safer.

Question 49

The spacing between the parallel power lines is affected by

A)current-carrying capacities of wires.
B)electrical insulation.
C)the wing span of birds in the vicinity.
D)none of the above

Question 50

An iron core in a transformer

A)guides magnetic field lines.
B)shields unwanted external electric or magnetic fields.
C)separates the primary and secondary regions.
D)reduces energy losses.

Question 51

A step-up transformer steps up voltage by ten times. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is

A)1 W.
B)10 W.
C)100 W.
D)1000 W.
E)none of the above

Question 52

The high voltage that is important in a power line is high voltage

A)between the parallel wires of the line.
B)from one end of each power line to the other.
C)both of these
D)neither of these

Question 53

Underlying the concept of self-induction is

A)Ohm's law.
B)Faraday's law.
C)Maxwell's law.
D)all of these about equally

Question 54

To reduce the danger of self-induction

A)simply pull the circuit plug.
B)turn off the switch to the circuit.
C)either of these
D)neither of these

Question 55

The voltage across the input terminals of a transformer is 120 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer delivers is

A)30 V.
B)60 V.
C)120 V.
D)240 V.
E)none of the above

Question 56

Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 120 V. What is the power output of the secondary coil?

A)30 W
B)120 W
C)480 W
D)960 W
E)need more information

Question 57

Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be

A)1 primary to 100 secondary.
B)100 primary to 1 secondary.
C)neither of these

Question 58

The primary of a transformer

A)has an iron core.
B)may or may not have an iron core.
C)has more turns of wire than the secondary.
D)none of the above

Question 59

The voltage across the input terminals of a transformer is 120 V. The primary has 25 loops and the secondary has 50 loops. The voltage the transformer delivers is

A)30 V.
B)60 V.
C)120 V.
D)240 V.
E)none of the above

Question 60

The transmission of power from one place to another is evident in

A)household electricity.
B)radio broadcast.
C)mobile phones.
D)all of the above

Question 61

High-voltage wires in power lines are not high-current wires because the current in them is

A)not the same as the current that powers the distant load.
B)proportional to the voltage drop from beginning to end of each line, rather low.
C)both of these
D)neither of these

Question 62

In the field induction credited to Maxwell, wires

A)can be insulated or non-insulated.
B)are minimized.
C)are not needed.

Question 63

A friend says that changing electric and magnetic fields underlie the production of light.

A)agree with your friend
B)argue to the contrary with your friend.
C)find a new friend.

Question 64

The strength of an induced electric or magnetic field depends on

A)strength of magnetic poles.
B)alignment of magnetic domains.
C)rate of change of the induced field.
D)all of the above
E)none of the above

Question 65

Induced electric and magnetic fields result in

A)electromagnetic waves.
B)stronger electric or magnetic fields.
C)higher voltages produced by Faraday induction.
D)all of the above
E)none of the above

Question 66

Rapid change of a magnetic field induces

A)a magnetic field of greater magnitude.
B)a magnetic field of the same magnitude.
C)an electric field.

Question 67

Faraday's law was extended by Maxwell toward

A)changes in electric fields.
B)changes in magnetic fields.
C)both of these
D)neither of these

Question 68

A force field is induced in any region of space in which

A)an electric field changes with time.
B)a magnetic field changes with time.
C)both of these
D)neither of these

Question 69

The induced electric and magnetic fields of Maxwell are

A)parallel to each other.
B)perpendicular to each other.
C)non-directional.

Question 70

When voltage is stepped up in a transformer, current is stepped down. But Ohm's law tells us that greater voltage means greater current, not less current. How then can current be lower when voltage is increased?

A)Current in the secondary is lower when compared to the greater current drawn by the primary.
B)Ohm's law applies to the circuit connected to the secondary, not to the transformer.
C)both of these
D)neither of these