chp 25 h/w
Terms in this set (30)
What important discovery did physicists Michael Faraday and Joseph Henry make?
What must change in order for electromagnetic induction to occur in a wire coil?
The magnetic field through the coil must change.
State Faraday's law.
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.
What are the three ways in which voltage can be induced in a loop of wire?
Move a magnet near the loop, move the loop near a magnet, change current in a nearby loop
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
The frequencies are the same.
What are the basic differences and similarities between a generator and an electric motor?
In both, moving electrons experience a force. The motor transforms electrical energy to mechanical energy. The generator transforms mechanical energy to electrical energy
Is the current that is produced by a common generator ac or dc or some combination?
What is the common frequency of ac in homes in the United States?
Who discovered electromagnetic induction, and who put it to practical use?
Discovered by Faraday and Henry; put to use by Tesla and Westinghouse
What is an armature?
Iron cores wrapped with copper wire
What commonly supplies the energy input to a turbine?
Steam or falling water
Is it correct to say that a generator produces energy? Defend your answer.
Generators do not produce energy. Instead, they convert it from some other form to electrical energy
What are the principal differences between an MHD generator and a conventional generator?
The only moving part in an MHD generator is the plasma.
Does an MHD generator employ Faraday's law of induction? Explain.
No. There are no changing magnetic fields in an MHD generator.
What name is given to the rate at which energy is transferred?
Is it correct to say that a transformer boosts electric energy? Defend your answer.
No. Conservation of energy requires that the energy out is the same as energy in.
Which of these does a transformer change: voltage, current, energy, power?
Voltage and current
How does the power input to an efficient transformer compare with the power output?
Input power equals output power.
What exactly does a step-down transformer step down?
In a step-down transformer, how does the input current compare with the output current?
The output current is greater than the input current.
Why does a transformer require ac?
A voltage is induced only when the magnetic field is changing.
What is the principal advantage of ac over dc?
It is easy to step up and step down voltages using ac.
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?
What is the purpose of transmitting power at high voltages over long distances?
High voltages can be used to transmit power at low current, thus decreasing losses due to heating in the wire.
Does the transmission of electric energy require electrical conductors between the source and receiver? Cite an example to defend your answer.
No. Sunlight transports electromagnetic power to Earth through a vacuum.
Who extended Faraday's law to changing electric fields?
What is induced by the rapid alternation of a magnetic field?
A rapidly alternating electric field
What is induced by the rapid alternation of an electric field?
A rapidly alternating magnetic field
Are wires needed in Maxwell's view of Faraday's law?
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.
What do we call electromagnetic waves in the range of frequencies that match what our eyes can see?