Physics Chapter 9

25 July 2022
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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?
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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.
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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.
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N2N1 = 50
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The rule for the interaction of magnetic poles is similar to the rule for electric
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charges
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Unlike electric charges, magnetic poles cannot be
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isolated
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Like kinds of magnetic poles repel while unlike kinds of magnetic poles
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attract
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Every magnet contains at least
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two poles
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Refrigerator magnets
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have short range
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Break a bar magnet in half and each half is
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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
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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
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equally huge
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The source of all magnetism is
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moving electric charge.
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A magnetic field easily penetrates
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-plastic coatings. -human flesh. -*both
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Magnetism is due to the motion of electrons as they
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-move around the nucleus. -spin on their axes. -*both
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An iron rod becomes magnetic when
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the net spins of its electrons are in the same direction.
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An iron nail is more strongly attracted to the
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north or south pole-no difference.
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Magnetic domains normally occur in
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iron
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A bar magnet that holds a chain of nails illustrates
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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
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north pole
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When a bar magnet is broken in half, the magnetic strength of each piece is
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the same
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Magnetic field lines about a current-carrying wire
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circle the wire in closed loops.
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The magnetic field lines about a current-carrying wire form
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circles
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When the current in a wire is reversed, the direction of the surrounding magnetic field
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also reverses
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When a current-carrying wire in a magnetic field experiences no force it is likely
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parallel to the field lines.
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A magnetic field exists in a current-carrying coil of wire
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with or without a contained piece of iron.
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A magnetic field exists in a current-carrying coil of wire
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with or without a contained piece of iron.
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The magnetic field inside a current-carrying coil increases when
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-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
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iron rod
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An electromagnet consists of a
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current-carrying coil with a piece of iron inside.
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Superconducting electromagnets
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exist now
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A superconducting electromagnet makes use of
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low-resistance coils of wire
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Moving electric charges will interact with
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-an electric field. -a magnetic field. -*both
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Maximum magnetic force occurs when electrons move
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perpendicular to the magnetic field direction.
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The minimum magnetic force on a moving electron occurs for motion
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parallel to the magnetic field.
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A magnetic force acts most strongly on a current carrying wire when it
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-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
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deflecting them
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The intensity of cosmic rays bombarding the Earth's surface is largest at the
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poles
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A galvanometer measures
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electric current
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A galvanometer is a useful device in electric
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meters
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A galvanometer calibrated to read current is
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an ammeter.
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A galvanometer calibrated to read potential difference is
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a voltmeter.
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An electric motor and electric generator are
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very similar devices.
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An electric motor and electric generator differ in
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the roles of input and output.
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A device that transforms electrical energy to mechanical energy is a
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motor
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A device that transforms mechanical energy to electrical energy is a
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generator
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Since magnetic force is always perpendicular to moving charges, magnetic force can only change an electron's
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direction
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Which force field can increase a moving electron's speed?
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electric field
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Electromagnetic induction was discovered by
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-Michael Faraday -Joseph Henry
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Faraday's law is the law that describes
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electromagnetic induction.
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Electromagnetic induction occurs in a coil when there is a change in
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magnetic field intensity in the coil
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Voltage can be induced in a wire by
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-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
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-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
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-current. -voltage. -*both
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Changing the magnetic field intensity in a closed loop of wires induces
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-current. -voltage. -*both
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When a magnet is thrust into a coil of wire, a greater voltage is induced
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-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
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twice as much.
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When a magnet is thrust into a coil of wire, the coil tends to
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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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Faraday's law
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Electromagnetic induction is employed in
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-credit cards. -iPads. -computers
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Alternating current is normally produced by a
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generator
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Which of these statements is true?
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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
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-current. -voltage. -*both
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Voltage produced by a generator alternates because
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the magnetic field that produces it alternates.
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The main difference between a generator and a motor involves which terminal is
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-input. -output. -*both
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Power is the rate at which
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energy is transferred
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An electric generator of itself
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cannot produce energy, but convert energy of other forms to electric energy
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The energy source for a generator may be
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-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
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the conservation of energy.
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A transformer requires
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alternating voltage
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A transformer actually transforms
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energy from one value of voltage to another.
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The rate at which a transformer transfers energy is called
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power
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Compared with the power input to an ideal transformer, the power output is
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the same
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Compared with the voltage input to a transformer, the voltage output can be
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greater or less
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Transformers use ac so there will be the required
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change in magnetic field for operation.
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A step-down transformer decreases
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voltage
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Compared with the current in the primary coil of a transformer, the current in the secondary coil
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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
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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
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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
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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
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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?
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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
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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
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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
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84 V
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The rapid alteration of a magnetic field induces
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an electric field
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The rapid alteration of an electric field induces
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a magnetic field
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Maxwell's counterpart to Faraday's law simply states that
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each change in field induces the other
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The frequency of a generated electromagnetic wave matches the
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frequency of vibrating changes
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What field generation cannot create is
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energy
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We know that a compass points northward because Earth is a giant magnet. Does the northward-pointing needle point northward when the compass is brought to the Southern Hemisphere?
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yes
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When a current-carrying wire is placed in a strong magnetic field, no force acts on the wire. What orientation of the wire is likely
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Maximum force occurs when the wire is at 90 degrees to the field.