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DC THEORY
DC THEORY
DC THEORY
DC THEORY
DC THEORY
100
Materials that are resistant to corrosion, have free electrons that are easily moved, are flexible, and have low coefficiants for expasnsion are good what?
Conductors
100
Materials that protect against short circuits are called what?
Insulators
100
Materials that can function as a conductor or as an insulator, depending on the conditions of the circuit and the direction of current flow are called what?
Semi conductors
100
What is the unit of measurement of a quantity of electrons?
Coulomb
100
Current flow from poisitive to negative is called what?
The Conventional Theory
200
Current flow from negative to positive is called what?
The electron theory
200
What is the magnetic field around a wire that is caused by current flowing through the wire?
Electromagnetism
200
Which of the following devices or methods may be used to produce a voltage? Thermocouple, photocell, rotary converter, battery, transformer, rectifier, generator, two objects rubbing together, mercury tube, resistor, diode, SCR, Pressure applied to a crystal
Thermocouple Photocell Battery Generator Two Objects rubbing together Pressure applied to a crystal
200
What are four terms that might be used to indicate the presence of a voltage?
Difference in potential Electromotive force EMF Pressure
200
What are four factors that determine the resistance of a conductor?
Type of material Cross sectional area Length Temperature
300
What are three types of resistors?
Fixed Rheostat (adjustable with two terminals) Potentiometer (adjustable with three or more terminals)
300
What is the symbol and unit of measurement for current?
I Amperes
300
What is the symbol and unit of measurement for voltage?
E volts
300
What is the symbol and unit of measurement for resistance?
R Ohms
300
What is the symbol and unit of measurement for power?
P watts
400
What is the unit of measurement of electrons in motion?
Ampere
400
An ohmmeter reading obtained from an open circuit would read what?
Infinity
400
How does normal current flow change when a short circuit occurs? Why?
Current flow increases because the total circuit resistant decreases due to a "shorter" path.
400
What are two conditions which may indicate that a low voltage condition exists on a coal producing section using DC equipment?
Motors running slower and dim lights There may be an increase in the operating temperature of the equipment.
400
What is the function of a rectifier?
Converts AC to DC
500
What are three things that must be present in order for current to flow?
Conductor Difference in potential Complete circuit
500
What are the two basic types of electrical circuits?
Series and Parallel
500
What are three precautions an electrician must observe when measureing a DC voltage with a voltmeter?
Proper gloves Proper meter and scale Observe polarity of the test leads
500
Resistors are rated in what?
Ohms and watts
500

What happens as resistance in a series circuit is increased across a constant source of voltage?

Current decreases and wattage decreases