Page 83 - Apprentice Manual_Neat

S3-Q64. Change in flux over change in time or number of flux lines cut per unit time is what law?

a.) Ohm’s law
This is resistance, current flow, and voltage.
b.) *Faraday’s law
Correct. Michael Farady in 1831 discovered the law of electromagnetic induction. It revealed
the fundamental relationship between voltage output and flux input to a circuit. The resulting
formula is: E = N(ΔΦ/Δt) where N = # turns in the coil, ΔΦ=change in flux, and Δt = change in
time.
c.) Kirchoff’s law
This is the series and parallel voltage and current laws.
d.) Murphy’s law
It would be by Murphy’s law if you had selected this answer.

S3-Q65.) Brush type generators do NOT require which of the following components?
a.) *Exciter field
Correct. The exciter field is required for generators that use induction as a means to transfer
energy.
b.) 2-Slip rings
The brushes transfer the energy via the slip rings from the rotor.
c.) Main rotor
All generators require a main rotor.
d.) Brushes
It would not be a brush type generator if it did not require brushes.

S3-Q66.) Generators running without excitation will often experience residual voltage. This phenomenon is
due to.

a.) *Magnetism left over in the iron of the field.
Correct. Some residual magnetism is left in the iron of the generator after the field had been
removed. This is one of the properties of ferrous metals. Unless degaussing is performed, that
magnetism will never completely disappear.
b.) Static electricity in the air
Static electricity would have no effect on dynamic generators.
c.) Failure to properly short-out the field
Shorting the field is never a good idea.
d.) Corona effect
Not a phenomenon of a generating.

S3-Q67.) Rotating diodes are best tested with which of the following tools?

a.) Mega-Ohmmeter
Used to test the insulating properties of conductor insulation.
b.) Rotating diode tester specified by the generator manufacturer
While these may exist, they are not necessary.
c.) *DVOM
Correct. A standard Digital Volt Ohm Miliammeter will suffice. Many today also have a diode
testing feature, however, that feature is not necessary.
d.) Oscilloscope
This would require energizing the diode and is not necessary. A standard DVOM or analog VOM will
do very nicely.

Page 75 - EGSA Apprentice Certification Program Study Guide