UNIT 12 Flashcards
Continually and rapidly reversing current
Alternating current
Protects the circuit from an overload
Circuit breaker
Device used to measure resistance
Ohmmeter
Component that is neither a conductor or insulator but a partial conductor
Semiconductors
Coil of wire wrapped around an iron core that induces a current to another coil of wire wrapped around the same iron core
Transformer
Unit of power
Watts
Smallest amount of a substance that can exist
Atom
Used to measure current without breaking a circuit to install the meter
Clamp-on-meter
Amount of charge that can be stored
Capacitance
When an atom has more electrons than protons
Negative charge
Total voltage is applied across each resistance. Current is divided between the different loads and total current is equal to the sum of the currents in each branch. Total resistance is less than the value of the smallest resistance
Parallel circuit
Used to measure current in a circuit
Ammeter
Materials with few electrons in the outer orbit such as gold, silver, copper, and aluminum
Conductor
Has a negative charge and travels around the nucleus in orbits or shells
Electrons
Total effect of resistance in a circuit consists of pure resistance, inductive reactance, and capacitive reactance
Impedance
A resistor that is sensitive to temperature
Thermistor
A force causing a magnetic field to attract ferrous metals or where like poles of a magnet repel and unlike poles attract each other
Magnetism
May be used as a switch or as a device to amplify an electrical signal
Transistor
Voltage is divided across the different resistances. Total current flows through each resistance or load. Resistances are added together to obtain total resistance.
Series circuit
Device that allows heat to be dissipated into the surrounding air
Heat sink
True or false
In a capacitive circuit, volts lags current (ICE)
True
True or false
Total resistance of a parallel circuit is less than the value of the smallest resistance
True
True or false
Current in a series circuit is the same regardless of where it is measured
True
In a pure resistive circuit, voltage leads current
False
True or false
If wire is wound into a coil and a current is passed through it, the coil, carrying an electrical current is called a solenoid/electromagnet
True
True or false: Electrons flow from positive to negative in a direct current (DC) circuit.
False
True or false: Inductive loads primarily generate a magnetic field whereas resistive loads generate light and/or heat.
True
True or false: Lightbulbs in a series circuit will all have the same brightness regardless of the resistance in each light bulb.
False
True or false: As resistance in a circuit increases, current decreases.
True
True or false: A rectifier is used to change AC current into DC current.
True
The full load amperage (FLA) rating on a fan motor data plate is 1.5A. What is the lock, rotor amperage (LRA) for the fan motor?
FLA 1.5 x 5= 7.5 LRA
The proper way to discharge a capacitor before testing it is to use a resistor that has a resistance of __________K ohms and rated for _________W.
20K ohms and rated for 5 watts
How are the three terminals on a dual capacitor marked?
Common, fan, herm
As temperature in a wire increases, resistance………
Increases
2 lightbulbs, 25 watts and 100 watts, are wired in parallel and powered by 116V power supply. What is the total current and total resistance for the circuit?
E= 116V
I= 1.07A
R= 108.41 ohms
P= 125 watts
What would the voltage in a DC circuit be if there were a current flow of .5A and a load resistance of 50 ohms?
E= 25V
Draw the electrical symbol for a temperature switch that closes on the rise, commonly used in a cooling thermostat
Draw the electrical symbol for an air core transformer
What component is an example of electromagnetic induction?
Transformer
The insulating material between the two conductive plates in a capacitor is called the……
Dielectric
If peak voltage measured is 294.20v, what is the root means square (RMS) value?
PV x 0.707 = 294.20v x 0.707= 207.9994 (208 rounded)
For forward bias orientation of a diode, the negative terminal on the battery should be connected to the……
Cathode
A positive temperature coefficient (PTC) thermistor’s resistance ____________ as temperature ___________
Increases, increases
Which wire size can carry the greatest amount of current?
8 AWG
Explain how a PTC thermistor can be used to protect a motor
By acting as a temperature-sensitive switch, PTC’s protect motors from overloading
Three capacitors rated at 3 micro ferrets, 40 micro ferret, and 300 micro ferrets are connected in parallel in a circuit with a 120v power supply. What is the total capacitance for the circuit?
3+40+300= 343 micro ferrets
The meter used to measure DC current couldn’t detect the current flow in the circuit. What can be done to amplify the current so the meter can measure the current?
Wrap coil in increments of ten. The reading will then need to be divided by ten to achieve the accurate reading.
A step down transformer is rated 60VA, input voltage is 120/208/240v at 50/60 Hz. Output voltage is 24v. What is the maximum current that the transformer can handle without being damaged?
60VA/ 24V= 2.5 A
Meter is set to volts AC. Test probes are placed at point 1 and 9. What is the expected meter reading?
115v
Meter is set to ohms. Meter test probes are placed at point 5 and 6. What is the expected meter reading?
O.L. (Open line)
The power is off. Meter is set to ohms .point 9 is disconnected from the circuit and meter probes are placed at point 7 and 8. what is the expected meter reading?
O.L. (Open line)
The switch labeled “D” is what type of switch and where would it be used for in a circuit?
Cooling thermostat
Used to maintain a specific temperature
A transformer that has more windings in the secondary than the primary is known as a ______________.
Step down transformer
