What important discovery did physicists Michael Faraday and Joseph Henry make?
answer
Electromagnetic induction
question
What must change in order for electromagnetic induction to occur in a wire coil?
answer
The magnetic field through the coil must change.
question
State Faraday's law.
answer
The induced voltage in a coil is proportional to the number of loops, to the area of the loops, and to the rate of change of the magnetic field through the loops.
question
What are the three ways in which voltage can be induced in a loop of wire?
answer
Move a magnet near the loop, move the loop near a magnet, change current in a nearby loop
question
How does the frequency of induced voltage relate to how frequently one pole of a magnet is plunged in and out of a coil of wire
answer
The frequencies are the same.
question
What are the basic differences and similarities between a generator and an electric motor?
answer
In both, moving electrons experience a force. The motor transforms electrical energy to mechanical energy. The generator transforms mechanical energy to electrical energy
question
Is the current that is produced by a common generator ac or dc or some combination?
answer
ac
question
What is the common frequency of ac in homes in the United States?
answer
60 hz
question
Who discovered electromagnetic induction, and who put it to practical use?
answer
Discovered by Faraday and Henry; put to use by Tesla and Westinghouse
question
What is an armature?
answer
Iron cores wrapped with copper wire
question
What commonly supplies the energy input to a turbine?
answer
Steam or falling water
question
Is it correct to say that a generator produces energy? Defend your answer.
answer
Generators do not produce energy. Instead, they convert it from some other form to electrical energy
question
What are the principal differences between an MHD generator and a conventional generator?
answer
The only moving part in an MHD generator is the plasma.
question
Does an MHD generator employ Faraday's law of induction? Explain.
answer
No. There are no changing magnetic fields in an MHD generator.
question
What name is given to the rate at which energy is transferred?
answer
Power
question
Is it correct to say that a transformer boosts electric energy? Defend your answer.
answer
No. Conservation of energy requires that the energy out is the same as energy in.
question
Which of these does a transformer change: voltage, current, energy, power?
answer
Voltage and current
question
How does the power input to an efficient transformer compare with the power output?
answer
Input power equals output power.
question
What exactly does a step-down transformer step down?
answer
Voltage
question
In a step-down transformer, how does the input current compare with the output current?
answer
The output current is greater than the input current.
question
Why does a transformer require ac?
answer
A voltage is induced only when the magnetic field is changing.
question
What is the principal advantage of ac over dc?
answer
It is easy to step up and step down voltages using ac.
question
When the magnetic field changes in a coil of wire, voltage in each loop of the coil is induced. What is the name of the voltage induced in a loop if the source of the magnetic field is the coil itself?
answer
Self-induction
question
What is the purpose of transmitting power at high voltages over long distances?
answer
High voltages can be used to transmit power at low current, thus decreasing losses due to heating in the wire.
question
Does the transmission of electric energy require electrical conductors between the source and receiver? Cite an example to defend your answer.
answer
No. Sunlight transports electromagnetic power to Earth through a vacuum.
question
Who extended Faraday's law to changing electric fields?
answer
Maxwell
question
What is induced by the rapid alternation of a magnetic field?
answer
A rapidly alternating electric field
question
What is induced by the rapid alternation of an electric field?
answer
A rapidly alternating magnetic field
question
Are wires needed in Maxwell's view of Faraday's law?
answer
Electromagnetic waves of radio travel through air.
Electromagnetic waves from automobile headlights travel through air.
Electromagnetic waves of sunlight travel through the vacuum of space.
-> All of the above.
question
What do we call electromagnetic waves in the range of frequencies that match what our eyes can see?
answer
Visible light
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