Ohm's Law

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  1. Electrical pressure is measured in what?
    volts
  2. A thermocoupler will transform what into electricity and is used where?
    Heat. Is used in a water heater as a switch.
  3. A rectifier is used to change what?

    What must be used to solve what problem created by a bridge rectifier used to turn AC into DC?
    • AC to DC. I.e. full wave rectifiers and not a half wave rectifier.
    • A capacitor in parallel with a resistor can be used to level out the pulsating dc current into a filtered DC current.
    • Connecting four rectifiers into the full-wave rectifier circuit shown provides a bridge circuit which allows different rectifiers to alternately provide current to the load during each half of the sine wave alternation, while always keeping the same direct-current polarity on the load. This provides a partial solution, however the current produced is not a pure dc current, but what’s called “pulsating dc current”
    • Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 69
  4. Capacitance is measured in what?
    Farads
  5. Capacitance Reactance is measured in what?
    ohms
  6. Storage batteries are rated in what? And based on a discharge rate for how many hours?
    amp-hours and usually at 20 hours discharge rate versus a starting battery that uses a 10 hours discharge rating.

    explained: because of the Peukert effect (aka, The faster a battery is drained, the less overall amperage is available), if you discharge a battery over the course of 100 hours, the AH rating looks higher that if you discharge that same battery over the course of 1 hour. So, there has to be a standard.  For deep cycle batteries the standard rating is 20 hours. So, if a battery has a rating of 100AH @ 20 Hr rate, then that battery was discharged over 20 hours with a 5 amp load.  Starting batteries on the other hand, are typically rated at 10Hr rate, because they are used faster, so the 20Hr rate is not as important. 
  7. It is customary to speak of the electromotive force as the ________of the circuit.
    voltage
  8. Electricity produced by means of a pressure to a material is called?
    piezoelectricity.  An example is FLE switching used in title 24 California advanced lighting which uses milliamps from finger pressure to wirelessly signal a light to switch via a load controller.  This removes the travelers and wire otherwise necessary.
  9. The insulation material in the commmutator of a DC generator between the positive and negative bars is made of?
    • Mica
  10. An A.C. generator is also called what?
    An alternator.
  11. A DC generator can be built with much larger voltage ratings than AC? T or F
    False.  Remember a DC generator uses a commutator and this limits the amount of current output. Peak voltage is 1.414 times RMS or effective multiplied by 2 again equals AC peak to peak. This would be the same as 2.828 times RMS or effective which is essentially DC.  In other words an AC revolving field generator can produce 2.28 times the voltage of a DC generator but produce the same heating effect.
  12. A voltmeter measures what?
    The effective voltage difference, which can be line to ground, line to neutral, or line to line.  And is always placed in parallel with the circuit.
  13. What is the most widely used generator today?
    Revolving field AC generator.  The term generator is misleading.   Here is why.


    • Generator is a generic class of devices, while the alternator is a type of generator producing AC current.
    • • Alternators use voltage regulators and rectifiers to create a DC output, while in other generators DC current is obtained by adding a commutator or AC current is produced.
    • • Alternator output can have varying frequencies due to changes in the rotor frequency (but it has no effect because the current is rectified to DC), while the other generators are operated to a constant frequency of the rotor shaft.
    • • Alternators are used in automobiles, to generate electrical power.
  14. A voltmeter is connected in what way with the circuit? Versus an ammeter?
    parallel is the way in which this is connected to a circuit.  An ammeter is connected in series in only a DC circuit where a clamp-on CT or clamp style ammeter is used in AC.  However induction can be picked up with a CT, but only when the load is pulling current.  CURRENT SHOULD NEVER BE CHECKED TO SEE IF A CIRCUIT IS ENERGIZED OR NOT.
  15. What is measured in henrys?
    inductance
  16. Inductive reactance is measured in what?
    ohms
  17. A generator exciter uses what type of current?
    Direct
  18. A nuetral carries what? So a broken neutral will always have higher or lower voltage across the lower watt load?
    The unbalanced load back to the source. A broken nuetral will always have a higher voltage across the lower watt source.
  19. Ohm's law applies only to what type of circuit?
    Purely resistive.
  20. What operates under the principal of electro-chemistry?
    batteries operate under this principal.  

    The NEC under article 480 and definitions has a fine print note that denotes “The most common nominal cell voltage 2 volts per cell for the lead-acid systems, 1.2 volts cell for alkali systems, and 3.6 to 3.8 volts per cell for Li-ion systems. Nominal voltages might vary with different chemistries.” 
  21. Resistance is proportional to length and diameter of a conductor how?
    • Resistance is directly proportional to length and inversely proportional to diameter of this.
    • Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
  22. These currents are stray currents that consume power and oppose current flow. They are produced by the expanding and collapsing magnetic field of alternating current circuits.
    • Eddy currents are produced by these.
    • Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
  23. When the conductor is _______, the flux lines cut through the conductor at more than point. This increases the CEMF by self-induction.
    • When the conductor is coiled this happens with regards to magnetic flux.
    • Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76

Card Set Information

Author:
johnbowens
ID:
111792
Filename:
Ohm's Law
Updated:
2017-04-22 17:39:26
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Ohm law
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Description:
NJATC Ohm's law 4th year of a 5 yr program. Taken from tests
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