# Physics Chapter 9

## Unlock all answers in this set

question
Magnet A has twice the magnetic field strength of magnet B, and at a certain distance it pulls on magnet B with a force of 50 N. With how much force does magnet B then pull on magnet A?
50 N
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A transformer for a laptop computer converts a 120-V input to a 24-V output. Find the ratio of the number of turns in the primary and the secondary coil.
N1N2 = 5
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Neon signs require about 12,000 V for their operation. Consider a neon-sign transformer that operates off 240-V lines.
N2N1 = 50
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The rule for the interaction of magnetic poles is similar to the rule for electric
charges
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Unlike electric charges, magnetic poles cannot be
isolated
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Like kinds of magnetic poles repel while unlike kinds of magnetic poles
attract
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Every magnet contains at least
two poles
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Refrigerator magnets
have short range
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Break a bar magnet in half and each half is
a complete magnet.
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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
exactly 100 N.
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Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is
equally huge
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The source of all magnetism is
moving electric charge.
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A magnetic field easily penetrates
-plastic coatings. -human flesh. -*both
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Magnetism is due to the motion of electrons as they
-move around the nucleus. -spin on their axes. -*both
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An iron rod becomes magnetic when
the net spins of its electrons are in the same direction.
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An iron nail is more strongly attracted to the
north or south pole-no difference.
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Magnetic domains normally occur in
iron
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A bar magnet that holds a chain of nails illustrates
magnetic induction
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Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a
north pole
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When a bar magnet is broken in half, the magnetic strength of each piece is
the same
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Magnetic field lines about a current-carrying wire
circle the wire in closed loops.
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The magnetic field lines about a current-carrying wire form
circles
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When the current in a wire is reversed, the direction of the surrounding magnetic field
also reverses
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When a current-carrying wire in a magnetic field experiences no force it is likely
parallel to the field lines.
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A magnetic field exists in a current-carrying coil of wire
with or without a contained piece of iron.
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A magnetic field exists in a current-carrying coil of wire
with or without a contained piece of iron.
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The magnetic field inside a current-carrying coil increases when
-the number of loops of wire in the coil increases. -current is increased. -*both.
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The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
iron rod
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An electromagnet consists of a
current-carrying coil with a piece of iron inside.
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Superconducting electromagnets
exist now
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A superconducting electromagnet makes use of
low-resistance coils of wire
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Moving electric charges will interact with
-an electric field. -a magnetic field. -*both
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Maximum magnetic force occurs when electrons move
perpendicular to the magnetic field direction.
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The minimum magnetic force on a moving electron occurs for motion
parallel to the magnetic field.
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A magnetic force acts most strongly on a current carrying wire when it
-is perpendicular to the magnetic field. -carries a very large current. -*either or both
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Earth's magnetic field affects cosmic rays by
deflecting them
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The intensity of cosmic rays bombarding the Earth's surface is largest at the
poles
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A galvanometer measures
electric current
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A galvanometer is a useful device in electric
meters
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A galvanometer calibrated to read current is
an ammeter.
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A galvanometer calibrated to read potential difference is
a voltmeter.
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An electric motor and electric generator are
very similar devices.
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An electric motor and electric generator differ in
the roles of input and output.
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A device that transforms electrical energy to mechanical energy is a
motor
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A device that transforms mechanical energy to electrical energy is a
generator
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Since magnetic force is always perpendicular to moving charges, magnetic force can only change an electron's
direction
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Which force field can increase a moving electron's speed?
electric field
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Electromagnetic induction was discovered by
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Faraday's law is the law that describes
electromagnetic induction.
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Electromagnetic induction occurs in a coil when there is a change in
magnetic field intensity in the coil
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Voltage can be induced in a wire by
-moving a magnet near the wire. -changing the current in a nearby wire. -moving the wire near a magnet. -*all of the above
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When a change of magnetic field occurs in a closed loop of wire
-a voltage is induced in the wire. -electromagnetic induction occurs. -current is made to flow in the loop of wire. -*all of the above
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Thrust a magnet into a coil of wire and you'll induce
-current. -voltage. -*both
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Changing the magnetic field intensity in a closed loop of wires induces
-current. -voltage. -*both
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When a magnet is thrust into a coil of wire, a greater voltage is induced
-with faster thrusting motion. -with a greater number of loops in the coil. -*both
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When a magnet is thrust into a coil that has twice the number of loops, the induced voltage is
twice as much.
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When a magnet is thrust into a coil of wire, the coil tends to
repel the magnet as it enters.
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The metal detectors that travelers walk through at airports operate via
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Electromagnetic induction is employed in
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Alternating current is normally produced by a
generator
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Which of these statements is true?
a battery produces dc and a generator produces ac
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The frequency with which a magnet plunges into and out of a magnetic field equals the frequency of the induced
-current. -voltage. -*both
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Voltage produced by a generator alternates because
the magnetic field that produces it alternates.
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The main difference between a generator and a motor involves which terminal is
-input. -output. -*both
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Power is the rate at which
energy is transferred
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An electric generator of itself
cannot produce energy, but convert energy of other forms to electric energy
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The energy source for a generator may be
-a waterfall. -wind. -steam from a turbine. -*any of these
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A topic that most underlies electrical studies and all of physics is
the conservation of energy.
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A transformer requires
alternating voltage
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A transformer actually transforms
energy from one value of voltage to another.
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The rate at which a transformer transfers energy is called
power
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Compared with the power input to an ideal transformer, the power output is
the same
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Compared with the voltage input to a transformer, the voltage output can be
greater or less
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Transformers use ac so there will be the required
change in magnetic field for operation.
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A step-down transformer decreases
voltage
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Compared with the current in the primary coil of a transformer, the current in the secondary coil
can be greater or less
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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
55 V
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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
220 V
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A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is
5A
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If the primary of a transformer were connected to a dc power source, the transformer would have a voltage output
only briefly while being connected or disconnected.
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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?
440 W
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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
120 V
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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
25 turns
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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
84 V
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The rapid alteration of a magnetic field induces
an electric field
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The rapid alteration of an electric field induces
a magnetic field
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Maxwell's counterpart to Faraday's law simply states that
each change in field induces the other
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The frequency of a generated electromagnetic wave matches the