P199 Ch 9
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
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
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
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
A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is
5 A
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
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
The metal detectors that travelers walk through at airports operate via
Faraday's law
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?
Maximum force occurs when the wire is at 90 degrees to the field
Electromagnetic induction was discovered by
Michael Faraday Joseph Henry
Which of these statements is true?
a battery produces dc and a generator produces ac
Break a bar magnet in half and each half is
a complete magnet
The rapid alteration of an electric field induces
a magnetic field
Surrounding every moving electron is
a magnetic field and an electric field
A galvanometer calibrated to read potential difference is
a voltmeter
When the current in a wire is reversed, the direction of the surrounding magnetic field
also reverses
A transformer requires
alternating voltage
A galvanometer calibrated to read current is
an ammeter
The rapid alteration of a magnetic field induces
an electric field
Moving electric charges will interact with
an electric field and magnetic field
Like kinds of magnetic poles repel while unlike kinds of magnetic poles
attract
Compared with the current in the primary coil of a transformer, the current in the secondary coil
can be greater or less
An electric generator of itself
cannot produce energy, but convert energy of other forms to electric energy
Transformers use ac so there will be the required
change in magnetic field for operation
Voltage can be induced in a wire by
changing the current in a nearby wire, moving a magnet near the wire, moving the wire near a magnet (all of the above)
The rule for the interaction of magnetic poles is similar to the rule for electric
charges
Magnetic field lines about a current-carrying wire
circle the wire in closed loops
The magnetic field lines about a current-carrying wire form
circles
Surrounding our planet Earth are
cosmic rays and magnetic fields
The frequency with which a magnet plunges into and out of a magnetic field equals the frequency of the induced
current and voltage (both)
Thrust a magnet into a coil of wire and you'll induce
current and voltage (both)
The magnetic field inside a current-carrying coil increases when
current is increased and the number of loops of wire in the coil increases
When a change of magnetic field occurs in a closed loop of wire
current is made to flow in the loop of wire, electromagnetic induction occurs, a voltage is induced in the wire (all of the above)
An electromagnet consists of a
current-carrying coil with a piece of iron inside
Earth's magnetic field affects cosmic rays by
deflecting them
Since magnetic force is always perpendicular to moving charges, magnetic force can only change an electron's
direction
Maxwell's counterpart to Faraday's law simply states that
each change in field induces the other
A galvanometer measures
electric current
Which force field can increase a moving electron's speed?
electric field
Faraday's law is the law that describes
electromagnetic induction
What field generation cannot create is
energy
A transformer actually transforms
energy from one value of voltage to another
Power is the rate at which
energy is transferred
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
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
Superconducting electromagnets
exist now
The frequency of a generated electromagnetic wave matches the
frequency of vibrating charges
A device that transforms mechanical energy to electrical energy is a
generator
Alternating current is normally produced by a
generator
Compared with the voltage input to a transformer, the voltage output can be
greater or less
Refrigerator magnets
have short range
The main difference between a generator and a motor involves which terminal is
input and output
Electromagnetic induction is employed in
ipads computers and credit cards
Magnetic domains normally occur in
iron
The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
iron rod
A magnetic force acts most strongly on a current carrying wire when it
is perpendicular to the magnetic field and carries a very large current
Unlike electric charges, magnetic poles cannot be
isolated
A superconducting electromagnet makes use of
low-resistance coils of wire
Electromagnetic induction occurs in a coil when there is a change in
magnetic field intensity in the coil
A bar magnet that holds a chain of nails illustrates
magnetic induction
A galvanometer is a useful device in electric
meters
A device that transforms electric energy to mechanical energy is a
motor
Magnetism is due to the motion of electrons as they
move around the nucleus and spin on their axes
The source of all magnetism is
moving electric charge
An iron nail is more strongly attracted to the
north or south pole-no difference
Several paper clips dangle from the north pole of a magnet. The included pole in the bottom of the lowermost paper clip is a
north pole
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
When a current-carrying wire in a magnetic field experiences no force it is likely
parallel to the field lines
The minimum magnetic force on a moving electron occurs for motion
parallel to the magnetic field
Maximum magnetic force occurs when electrons move
perpendicular to the magnetic field direction
A magnetic field easily penetrates
plastic coatings and flesh
The intensity of cosmic rays bombarding the Earth's surface is largest at the
poles
The rate at which a transformer transfers energy is called
power
When a magnet is thrust into a coil of wire, the coil tends to
repel the magnet as it enters
A topic that most underlies electrical studies and all of physics is
the conservation of energy
Voltage produced by a generator alternates because
the magnetic field that produces it alternates
An iron rod becomes magnetic when
the net spins of its electrons are in the same direction
An electric motor and electric generator differ in
the roles of input and output
Compared with the power input to an ideal transformer, the power output is
the same
When a bar magnet is broken in half, the magnetic strength of each piece is
the same
When a magnet is thrust into a coil that has twice the number of loops, the induced voltage is
twice as much
Every magnet contains at least
two poles
An electric motor and electric generator are
very similar devices
A step-down transformer decreases
voltage
Changing the magnetic field intensity in a closed loop of wires induces
voltage and current (both)
The energy source for a generator may be
wind, stem, waterfall (all)
When a magnet is thrust into a coil of wire, a greater voltage is induced
with a greater number of loops in the coil and with a faster thrusting motion (both)
A magnetic field exists in a current-carrying coil of wire
with or without a contained piece of iron
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?
yes