Preview Extract
Chapter 9 Magnetism and Electromagnetic Induction
9.1 Magnetic Poles
1) The rule for the interaction of magnetic poles is similar to the rule for electric
A) circuits.
B) polarization.
C) charges.
Answer: C
2) Unlike electric charges, magnetic poles cannot be
A) located.
B) isolated.
C) destroyed.
Answer: B
3) Like kinds of magnetic poles repel while unlike kinds of magnetic poles
A) attract.
B) repel also.
C) may attract or repel.
Answer: A
4) Every magnet contains at least
A) one pole.
B) two poles.
C) two or more poles.
Answer: B
5) Refrigerator magnets
A) have short range.
B) are without magnetic poles.
C) both
Answer: A
6) Break a bar magnet in half and each half is
A) a complete magnet.
B) a stronger magnet.
C) no longer magnetized.
Answer: A
7) Magnet A has twice the magnetic field strength of magnet B and pulls on magnet B with a
force of 100 N. The amount of force that magnet A exerts on magnet B is
A) at or about 50 N.
B) exactly 100 N.
C) more than 100 N.
D) not enough information
Answer: B
8) Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack
exerts on the magnet is
A) relatively small.
B) equally huge.
C) not enough information
Answer: B
9.2 Magnetic Fields
1) The source of all magnetism is
A) tiny bits of iron.
B) tiny domains of aligned atoms.
C) ferromagnetic materials.
D) moving electric charge.
Answer: D
2) Every spinning electron is
A) electrically charged.
B) is a tiny magnet.
C) both
D) none of the above
Answer: C
3) A magnetic field easily penetrates
A) human flesh.
B) plastic coatings.
C) both
D) none of the above
Answer: C
4) Surrounding every moving electron is
A) a magnetic field.
B) an electric field.
C) both
D) neither
Answer: C
5) Magnetism is due to the motion of electrons as they
A) move around the nucleus.
B) spin on their axes.
C) both
D) neither
Answer: C
6) An iron rod becomes magnetic when
A) positive ions accumulate at one end and negative ions at the other end.
B) its atoms are aligned with positive charges on one side and negative charges on the other side.
C) the net spins of its electrons are in the same direction.
D) electron motion stops.
E) none of the above
Answer: C
7) What is the cause of a magnetic field about a permanent magnet, and about a current-carrying
wire?
Answer: All magnetic fields have their origin in moving electric charges. About a permanent
magnet the moving charges are the electrons in the atoms making up the magnet-most commonly
iron atoms. About a current-carrying wire, the moving electrons produce the magnetic field.
9.3 Magnetic Domains
1) An iron nail is more strongly attracted to the
A) north pole of a magnet.
B) south pole of a magnet.
C) north or south pole-no difference.
Answer: C
2) Magnetic domains normally occur in
A) iron.
B) copper.
C) silver.
D) all of the above
E) none of the above
Answer: A
3) A magnet will become weaker if it is
A) dropped on a hard surface.
B) held in a hot flame.
C) either
D) neither
Answer: C
4) A bar magnet that holds a chain of nails illustrates
A) magnetic field displacement.
B) magnetic induction.
C) electromagnetic induction.
Answer: B
5) Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of
the lowermost paper clip is a
A) north pole.
B) south pole.
C) north or south pole-no difference.
Answer: A
6) 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.
Answer: C
9.4 Electric Currents and Magnetic Fields
1) Magnetic field lines about a current-carrying wire
A) extend radially from the wire.
B) circle the wire in closed loops.
C) both
D) neither
Answer: B
2) The magnetic field lines about a current-carrying wire form
A) circles.
B) radial lines.
C) eddy currents.
D) spirals.
Answer: A
3) When the current in a wire is reversed, the direction of the surrounding magnetic field
A) also reverses.
B) remains steady.
C) collapses.
Answer: A
4) When a current-carrying wire in a magnetic field experiences no force it is likely
A) upside down relative to the field.
B) overly insulated.
C) parallel to the field lines.
D) all of the above
Answer: C
5) A magnetic field exists in a current-carrying coil of wire
A) if it contains a piece of iron.
B) with or without a contained piece of iron.
C) only if the current changes.
Answer: B
6) The magnetic field inside a current-carrying coil increases when
A) current is increased.
B) the number of loops of wire in the coil increases.
C) both.
D) none of the above
Answer: C
7) The 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) iron rod.
E) none of the above
Answer: D
8) An electromagnet consists of a
A) bar magnet that carries an electric current.
B) coil of wire.
C) current-carrying coil with a piece of iron inside.
Answer: C
9) Superconducting electromagnets
A) exist now.
B) may be possible in the near future.
C) are not possible.
D) are science fiction.
Answer: A
10) 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.
Answer: A
11) Distinguish between a common bar magnet and an electromagnet.
Answer: A common bar magnet is usually composed of iron atoms, which produce the magnetic
field via the motion of their electrons. An electromagnet is a coil of wire, usually wrapped
around a piece of iron, that gets its magnetism from the electric current in the coil.
9.5 Magnetic Forces on Moving Charges
1) Moving electric charges will interact with
A) an electric field.
B) a magnetic field.
C) both
D) none of the above
Answer: C
2) Maximum magnetic force occurs when electrons move
A) in the same direction as the magnetic field.
B) opposite to the magnetic field direction.
C) perpendicular to the magnetic field direction.
D) at an angle other than 90° to the magnetic field direction.
E) none of the above
Answer: C
3) The minimum magnetic force on a moving electron occurs for motion
A) parallel to the magnetic field.
B) perpendicular to the magnetic field.
C) at an angle other than 90° to the magnetic field.
Answer: A
4) 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
D) none of the above
Answer: C
5) No magnetic force acts on a current carrying wire when it
A) carries a very small current.
B) is perpendicular to the magnetic field.
C) either or both
D) none of the above
Answer: D
6) Surrounding our planet Earth are
A) cosmic rays.
B) magnetic fields.
C) both
Answer: C
7) Earth's magnetic field affects cosmic rays by
A) deflecting them.
B) slowing their speeds.
C) destroying them.
D) absorbing them.
Answer: A
8) The intensity of cosmic rays bombarding the Earth's surface is largest at the
A) poles.
B) mid-latitudes.
C) equator.
Answer: A
9) A galvanometer measures
A) magnetic fields.
B) electric current.
C) electric voltage.
D) none of the above
Answer: B
10) A galvanometer is a useful device in electric
A) electromagnets.
B) transformers.
C) generators and motors.
D) meters.
E) none of the above
Answer: D
11) A galvanometer calibrated to read current is
A) an ammeter.
B) a voltmeter.
C) an ohm meter.
D) none of the above
Answer: A
12) A galvanometer calibrated to read potential difference is
A) an ammeter.
B) a voltmeter.
C) an ohm meter.
D) none of the above
Answer: B
13) An electric motor and electric generator are
A) very similar devices.
B) entirely different devices.
C) none of the above
Answer: A
14) An electric motor and electric generator differ in
A) the roles of input and output.
B) basic construction.
C) size.
D) quality.
Answer: A
15) A device that transforms electrical energy to mechanical energy is a
A) generator.
B) motor.
C) transformer.
D) magnet.
E) none of the above
Answer: B
16) A device that transforms mechanical energy to electrical energy is a
A) generator.
B) motor.
C) transformer.
D) magnet.
E) none of the above
Answer: A
17) Since magnetic force is always perpendicular to moving charges, magnetic force can only
change an electron's
A) speed.
B) direction.
C) speed and direction.
Answer: B
18) Which force field can increase a moving electron's speed?
A) electric field
B) magnetic field
C) both
D) neither
Answer: A
19) Which force field can both accelerate an electron and change its speed?
A) electric field.
B) magnetic field.
C) both
D) neither
Answer: A
20) What happens to a current-carrying wire in a magnetic field? How does orientation of the
wire make a difference?
Answer: Properly oriented, a current-carrying wire experiences a force when it is in a magnetic
field. The force is proportional to the magnetic field strength, the current in the wire, and the
orientation of the wire. When the wire is perpendicular to the magnetic field, force is maximum.
When the wire is parallel to the magnetic field, force is minimum-that is, zero. In between
parallel and perpendicular, the field varies between minimum and maximum.
9.6 Electromagnetic Induction
1) Electromagnetic induction was discovered by
A) Joseph Henry.
B) Michael Faraday.
C) both
D) neither
Answer: C
2) Faraday's law is the law that describes
A) electromagnetic induction.
B) the connection between current, voltage, and resistance.
C) the attraction and repulsion of magnetic poles.
D) the force between magnetic poles.
E) all of the above
Answer: A
3) 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) voltage in the coil.
D) the coil's polarity.
E) electromagnetic polarity.
Answer: B
4) 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: D
5) When a change of magnetic field occurs in a closed loop of wire,
A) a voltage is induced in the wire.
B) current is made to flow in the loop of wire.
C) electromagnetic induction occurs.
D) all of the above
E) none of the above
Answer: D
6) Thrust a magnet into a coil of wire and you'll induce
A) voltage.
B) current.
C) both
D) neither
Answer: C
7) Changing the magnetic field intensity in a closed loop of wires induces
A) current.
B) voltage.
C) both
D) neither
Answer: C
8) When a magnet is thrust into a coil of wire, a greater voltage is induced
A) with a greater number of loops in the coil.
B) with faster thrusting motion.
C) both
D) neither
Answer: C
9) When a magnet is thrust into a coil that has twice the number of loops, the induced voltage is
A) half.
B) the same, no different.
C) twice as much.
D) four times as much.
E) none of the above
Answer: C
10) When a magnet is thrust into a coil of wire, the coil tends to
A) attract the magnet as it enters.
B) repel the magnet as it enters.
C) both
D) neither
Answer: B
11) The metal detectors that travelers 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.
Answer: B
12) Metal detectors that locate metal beneath sand on a beach are activated by
A) electric fields.
B) magnetic fields.
C) electromagnetic induction.
D) alternating current.
Answer: C
13) Electromagnetic induction is employed in
A) credit cards.
B) computers.
C) iPads.
D) all of the above
E) none of the above
Answer: D
14) State Faraday's law of induction and explain what it means.
Answer: Faraday's law states that voltage induced across a coil is proportional to the rate at
which the magnetic field strength through the coil changes. It is also proportional to the number
of turns on the coil. This change can be brought about by rotating the coil, changing its shape, or
changing the magnetic field strength. Because of Faraday's law, current need not be restricted to
batteries, but can be induced in a wire by any of the changes stated. Faraday's law underlies
generators.
9.7 Generators and Alternating Current
1) Alternating current is normally produced by a
A) battery.
B) generator.
C) both
D) neither
Answer: B
2) Which of these statements is true?
A) a battery produces dc and a generator produces ac
B) a battery produces ac and a generator produces dc
C) a battery and a generator produce dc
D) a battery and a generator produce ac
Answer: A
3) The frequency with which a magnet plunges into and out of a magnetic field equals the
frequency of the induced
A) voltage.
B) current.
C) both
D) neither
Answer: C
4) Compared to a motor, a generator is
A) one and the same.
B) its opposite.
C) of an entirely different design.
Answer: B
5) Voltage produced by a generator alternates because
A) it produces pulses of current.
B) the magnetic field that produces it alternates.
C) alternations in the mechanical energy input.
D) in effect it is an ac motor in reverse.
E) the current it produces alternates.
Answer: B
6) The main difference between a generator and a motor involves which terminal is
A) input.
B) output.
C) both
Answer: C
7) 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) burned out.
D) none of the above
Answer: C
8) How are electric motors and electric generators similar? Different?
Answer: Both electric motors and generators are similarly-constructed devices. Both have a
permanent or electromagnet and coils of wire on a rotor. They differ mainly by the roles of input
and output. When input is electrical energy, the rotor is made to spin and we have a motor. When
input is mechanical energy, spinning the rotor, the output is electric voltage and we have a
generator.
9.8 Power Production
1) Power is the rate at which
A) energy is transferred.
B) voltage can be changed.
C) current can be induced.
Answer: A
2) An electric generator of itself
A) can produce enough energy to light cities.
B) cannot produce energy, but convert energy of other forms to electric energy.
C) neither
Answer: B
3) The sloshing of electrons inside a generator need
A) an outside source of energy.
B) a copper lattice.
C) positive ions.
D) none of the above
Answer: A
4) The energy source for a generator may be
A) a waterfall.
B) steam from a turbine.
C) wind.
D) any of these
E) none of the above
Answer: D
5) A topic that most underlies electrical studies and all of physics is
A) Newton's laws of motion.
B) the conservation of momentum.
C) the conservation of energy.
Answer: C
9.9 The Transformer-Boosting or Lowering Voltage
1) A transformer requires
A) alternating voltage.
B) direct current.
C) both
D) neither
Answer: A
2) A transformer actually transforms
A) energy from one value of voltage to another.
B) magnetic field lines.
C) generators into motors.
D) non-safe forms of energy to safe forms of energy.
E) all of the above
Answer: A
3) The rate at which a transformer transfers energy is called
A) electromagnetic induction.
B) transformer efficiency.
C) power.
Answer: C
4) Compared with the power input to an ideal transformer, the power output is
A) greater.
B) less.
C) greater or less.
D) the same.
Answer: D
5) Compared with the voltage input to a transformer, the voltage output can be
A) greater.
B) less.
C) greater or less.
Answer: C
6) Transformers use ac so there will be 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.
Answer: C
7) A step-up transformer increases
A) power.
B) energy.
C) both
D) neither
Answer: D
8) A step-down transformer decreases
A) current.
B) voltage.
C) power.
D) energy.
E) all of the above
Answer: B
9) Compared with the current in the primary coil of a transformer, the current in the secondary
coil
A) is greater.
B) is less.
C) can be greater or less.
D) none of the above
Answer: C
10) The voltage across the input terminals of a transformer is 110 V. The primary coil has 50
loops and the secondary has 25 loops. The output is
A) 25 V.
B) 55 V.
C) 110 V.
D) 220 V.
E) none of the above
Answer: B
11) The voltage across the input terminals of a transformer is 110 V. The primary coil has 50
loops and the secondary coil has 100 loops. The output is
A) 25 V.
B) 55 V.
C) 110 V.
D) 220 V.
E) none of the above
Answer: D
12) A certain transformer doubles input voltage. If the primary coil has 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
Answer: B
13) If the primary of a transformer were 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 briefly while being connected or disconnected.
E) none of the above
Answer: D
14) A current of 4 A exist in the primary coil of a transformer. The voltage across the primary
coil is 110 V. What is the power output of the secondary coil?
A) 27.5 W
B) 110 W
C) 440 W
D) 880 W
E) not enough information
Answer: C
15) An ideal transformer has 50 turns in the primary and 500 turns in the secondary. An input of
12 V will produce an output of
A) 120 V.
B) 10 times the power input.
C) both
D) neither
Answer: A
16) A transformer for a laptop computer converts a 120-V input to a 24-V output. Compared
with the number of turns on the primary coil, the secondary has
A) 1/5 as many turns.
B) 5 times as many turns.
C) the same number of turns.
D) none of the above
Answer: A
17) An electronic game requires 6 V for operation. A transformer allows it to be powered from a
120-V outlet. If the primary has 500 turns, the secondary has
A) 4 turns.
B) 25 turns.
C) 50 turns.
D) none of the above
Answer: B
18) A transformer has an input of 6 V and an output of 42 V. If the input is changed to 12 V, the
output would be
A) 12 V.
B) 48 V.
C) 84 V.
D) none of the above
Answer: C
19) What correction do you make to a friend who states that a step-up transformer boosts energy,
while a step-down transformer reduces energy in a circuit.
Answer: You remind your friend of the conservation of energy. Although a transformer can step
up or step down voltages and currents, in no way can it do the same with energy. Energy can
neither be created nor destroyed.
9.10 Field Induction
1) The rapid alteration of a magnetic field induces
A) an electric field.
B) a stronger magnetic field.
C) both
D) neither
Answer: A
2) The rapid alteration of an electric field induces
A) a stronger electric field.
B) a magnetic field.
C) both
D) neither
Answer: B
3) Maxwell's counterpart to Faraday's law simply states that
A) each change in field induces the other.
B) electric and magnetic fields are one and the same.
C) induced fields are parallel to each other.
Answer: A
4) Electric and magnetic fields combine to produce
A) sound.
B) light.
C) both
D) neither
Answer: B
5) The frequency of a generated electromagnetic wave matches the
A) field strength of the fields.
B) energy of the fields.
C) frequency of vibrating charges.
D) frequency of domains in the magnetic part of the wave.
Answer: C
6) What field generation cannot create is
A) light.
B) electromagnetic waves.
C) energy.
Answer: C
7) What is the connection, if any, between electromagnetic induction and sunshine?
Answer: Sunshine is light, which is part of the electromagnetic spectrum, all of which is
produced by accelerating electric charges. Vibrating charges in the Sun or any body constitute
vibrating electric currents, which induce vibrating magnetic fields, which induce...and so on. All
light is composed of electromagnetic waves, the result of electromagnetic induction.
Test Bank for Conceptual Physical Science
Paul Hewitt, John Suchocki, Leslie Hewitt
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