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Electricity
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Terms in this set (46)
Electricity
the flow of electrons in a conductor
Circuit
a path for an electrical current to flow around
Static
made of electrons that do not move
Current
made of moving electrons
Direct Current (DC)
current that only flows in one direction
Alternating Current (AC)
current that reverses the direction of flow many times each second
Conductors
Materials that transmit electricity
Insulators
Not good conductors of electricity and are sued to confine electricity
Service Entrance
where the electricity enters a building
Service Panel
houses the circuit breaker for the system and is used to distribute the power to individual circuits throughout the system
Overcurrent
exists when the current flow in a circuit exceeds the amperage rating of the circuits conductors or other devices
Circuit Breaker
heat-sensitive switch, which automatically trips when the electricity demand is so great that it causes the temperature of the conductor to get too hot
Fuse
have metal links that melt when the current flow is too great
GFCI (ground-fault circuit interrupter)
type of breaker that is extremely sensitive to circuit imbalances
National Electrical Code (NEC)
guidelines established to ensure the safe use of electricity
Voltage
the pressure in a circuit that causes the electrons or current to flow
Voltage Drop
when electricity must be carried a long distance through wires, there will be a decrease in voltage
Amperage
The amount of electrical current flowing past a point in a circuit
Watts
measure of electrical power
Kilowatts
units of 1,000 watts
Resistance
tendency of the wire to resist the flow of electrons or current through the wire
Ohms
measurement of resistance
Phase
timed source of electricity through a conductor
Single-phase
current from one source with three wires: one hot, one neutral, and one ground
Three-phase
three single phases combined
Resistance
A material's opposition to the flow of electric current.
voltage
the pressure in a circuit that causes the electrons or current flow
Ammeter
A device used to measure current in a circuit
Electromotive force (emf)
the force that results in the motion of electrons due to a difference in potential
Kilowatt-hour
a measure of electrical energy equivalent to a power consumption of 1,000 watts for 1 hour.
Ohmmeter
a device used to measure resistance
Power
the rate at which work is done
Power Equation
formula that defines the relationship between watts, amps,
and volts
3-way switch
Switches that controls a single load from two locations
4 way switch
Controls light from 3 or more locations
balanced load
means the
120 volt load should be approximately the same on each of the ungrounded
service conductors coming into the service entrance panel
branch circuits
originate in the service entrance panel and serve individual loads
or groups of loads
cable
consists of two or more wires in a protective outer sheath or jacket
conduit
channel or tube through which conductors are run in order to provide
the conductors with mechanical protection
Duplex Convenience Outlet
general purpose outlet having two receptacles built into one device
Feeder ciruits
originate in the service entrance panel and supply power to a
sub-panel
Individual Branch Circuit
the equipment connected to the SPO is the only load on that circuit
Special Purpose Outlet
outlet sized receptacle and is installed to serve a specific plug-and-cord connected appliance
Switch Loop
the wires from the lighting fixture to the switch
Throw
indicates the number of paths provided for current flow through the switch
Ungrounded Conductor
originates at the circuit breaker or fuse
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Verified questions
ENGINEERING
A hot liquid $(c_p = 1000 J/kg \cdot K)$ flows at a flow rate of 0.05 kg/s inside a copper pipe with an inner diameter of 45 mm and a wall thickness of 5 mm. At the pipe exit, the liquid temperature decreases by $10^\circ C$ from its temperature at the inlet. The outer surface of the 5-m-long copper pipe is black oxidized, which subjects the outer surface to radiation heat transfer. The air temperature surrounding the pipe is $10^\circ C.$ Assuming that the properties of air can be evaluated at $35^\circ C$ and 1 atm pressure, determine the outer surface temperature of the pipe. Is $35^\circ C$ an appropriate film temperature for evaluation of the air properties?
ENGINEERING
The quality of a two-phase liquid–vapor mixture of propane at 20 bar with a specific internal energy of $300 \: kJ/kg$ is $$ \begin{array}{l l } \text{(a) 0.166}\\ \text{(b) 0.214}\\ \text{(c) 0.575}\\ \text{(d) 0.627}\\ \end{array} $$
ENGINEERING
The maximum flow rate of standard shower heads is about 3.5 gpm( 13.3 L/min) and can be reduced to 2.75 gpm (10.5 L/min) by switching to low-flow shower heads that are equipped with flow controllers. Consider a family of four, with each person taking a 5-min shower every morning. City water at 15 $^\circ{}$C is heated to 55$^\circ{}$C in an electric water heater and tempered to 42$^\circ{}$C by cold water at the T-elbow of the shower before being routed to the shower heads. Assuming a constant specific heat of 4.18 kJ/kgK for water, determine (a) the ratio of the flow rates of the hot and cold water as they enter the T-elbow and (b) the amount of electricity that will be saved per year, in kWh, by replacing the standard shower heads with the low-flow ones.
ENGINEERING
An air conditioner with refrigerant-134a as the working fluid is used to keep a room at $26^{\circ} \mathrm{C}$ by rejecting the waste heat to the outside air at $34^{\circ} \mathrm{C}.$ The room is gaining heat through the walls and the windows at a rate of 250 kJ/min while the heat generated by the computer, TV, and lights amounts to 900 W. An unknown amount of heat is also generated by the people in the room. The condenser and evaporator pressures are 1200 and 500 kPa, respectively. The refrigerant is saturated liquid at the condenser exit and saturated vapor at the compressor inlet. If the refrigerant enters the compressor at a rate of 100 L/min and the isentropic efficiency of the compressor is 75 percent, determine (a) the temperature of the refrigerant at the compressor exit, (b) the rate of heat generation by the people in the room, (c) the COP of the air conditioner, and (d) the minimum volume flow rate of the refrigerant at the compressor inlet for the same compressor inlet and exit conditions.