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53 Cards in this Set

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  • Back
On a commercial basis, what is the overall heat-to-electricity conversion?
40% (1147)
What is the primary problem in the utilization of electric energy?
"The primary problem in the utilization of electric energy is that, unlike fuels or even heat, it cannot be readily stored and therefore must be generated and utilized in the same instant." (1147)
What is an ALTERNATOR?
"The bulk of electric energy utilized today is in the form of ALTERNATING CURRENT (ac), produced by generators commonly called ALTERNATORS." (1147)
What is DC electricity used for?
"...special applications requiring large quantities of DC...
"Smaller quantities of DC are utilizeded for...telephone and signal equipment, controls, and other specialized uses." (1147)
What is current?
"Electricity flowing in a conductor..." (1147)
How is current measured?
AMPERES (AMP or A) (1147)
How is current represented in an equation?
I or i (1147)
What is the analogy between mechanical (hydraulic) and electrical systems?
"Current is a measure of flow...corresponds to water flow...however, velocity of water flow varies, whereas...the velocity of (electric) propogation is constant and may be considered instantaneous." (1147)
What are the five system component analogies between electric and hydraulic systems?
"voltage is analogous to pressure,
current to flow,
friction to resistance,
wire to piping and
switches to valves." (1148)
What is electricity?
the energy of moving electrons (1148)
How is electricity caused?
"by creating a higher positive electric charge at one point on a conductor than exists at another point on the that same conductor." (1148)
What is the oldest and simplest way to create electricity?
"electrochemical action, as in a battery." (1148)
V or v
volt (1148)
What is voltage?
"...tendency for flow between the electrified particles concentrated at the positive and negative terminals." (1148)
What does voltage do?
"causes current to flow in a conductor connecting the terminals between which a voltage exists." (1148)
What is the relationship between voltage and current?
"The higher the voltage..., the higher the current... for a given resistance." (1148)
What is the OHM?
measure of resistance in a circuit (1148)
What materials display the least resistance (and so make good conductors)?
Metals
"The best conductors are the precious metals - silver, gold and platinum - with copper and aluminum being only slightly inferior." (1148)
What are INSULATORS?
"materials that resist the flow of current." (1148)
What materials are used to insulate electric conductors?
"Glass,
mica,
rubber,
oil,
distilled water,
porcelain, and
certain synthetics" (1148)
What are some common examples of insulated electrical components?
"rubber and plastic wire coverings,
porcelain lamp sockets, and
oil-immersed switches." (1148)
What is OHM'S LAW?
"The current I that will flow in a dc circuit is directly proportional to the voltage V and inversely proportional to the resistance R of the circuit." (1148)
What is the equation for Ohm's Law?
I = V/R
What are the two basic arrangements for electric circuits?
series
parallel (1149)
What are the characteristics of a series circuit?
"...the elements are connected one after the other...in series...
resistances and voltages add.
the current is the same in all parts of the circuit." (1149)
What are 4 characteristics of a parallel circuit?
"When two or more branches or loads in a circuit are connected between the same two points, they are said to be connected in parallel or multiple...
the voltage across each load is the same, but the current in each load (branch) depends upon the resistance of that load.
the total current in the circuit is the sum of the individual currents flowing in the branches...
The parallel connection is the standard arrangement in all building wiring." (1150)
What is the fundamental principle to remember in parallel circuits?
"... loads in parallel are additive for current...
each load has the same voltage across it." (1150)
What is a CIRCUIT?
"a complete conducting path that carries current from a source of electricity to and through some electrical device (or load) and back to the source." (class notes)
What is a SHORT CIRCUIT?
"If... a connection occurs between points A and B, the circuit is SHORTENED so that there is no resistance in parallel branch AB. The current rises instantly to a very high level and we have a SHORT CIRCUIT." (1151)
How are circuits protected from shorting and what happens if they are not protected?
"... a fuse or circuit breaker opens and the circuit is deenergized.
If not, the heat generated by the excessive current will probably start a fire." (1151)
What is dc (DIRECT CURRENT)?
"A flow of electric current that takes place at a constant time rate, practically unvarying and in the same direction around a circuit..." (1151)
What is ac (ALTERNATING CURRENT)?
"Whenever the flow of current is periodically varying in time and direction, as indicated by the symmetrical positive and negative loops, or SINE WAVES..." (1151)
Define: frequency (as relates to ac current)
"The number of cycles occurring in 1 second..." (1151)
Define: one cycle (as relates to ac current)
"The distance along the time axis spanned by a positive and negative ac loop..." (1151)
Define: hertz
cycles per second (1152)
What is the normal Hertz in the US and Canada ac systems?
60 Hz (1152)
Define: commutator
device attached to an ac generator that rectifies ac to dc. (1152)
What is Michael Faraday's principle of electromagnetic induction?
"...when an electrical conductor is moved in a magnetic field, a voltage is induced in the conductor.
The direction of the movement determines the polarity of the induced voltage...
If a conductor is formed into a coil and rotated in a magnetic field, a voltage of alternating polarity is produced, that is, alternating current." (1153)
In which direction does a current flow in a circuit?
positive to negative (1148)
In which direction does a current flow inside a battery?
negative to positive (1148)
What is the difference between power and energy?
"ENERGY is the technical term for the more common expression WORK.
POWER is the rate at which energy is used. Stated otherwise, it takes a fixed amount of energy to lift a weight a given distance either quickly or slowly, but the faster it is lifted, the more power that is required." (1153)
What is the mathematical relationship between energy (work) and power?
energy (work) = power x time
(1153)
How can energy be expressed?
"barrels of oil,
cubic feet of gas,
tons of coal,
kilowatt-hours of electricity usage,
dollars of fuel cost. (1153)
How is the outcome of energy efficiency efforts for buildings expressed?
"annual usage of oil, gas, and electricity, or...
dollars of fuel or utility costs." (1153)
What are the technical terms used to express energy?
Btu
kilowatt-hours (1153)
Define: Power
"...the rate at which energy is used or...
the rate at which work is done...
The term POWER implies continuity - that is, the use of energy at a particular rate, over a given, and generally considerable, span of time." (1153)
What term is synonymous with WORK?
ENERGY (1153)
What are typical units of power?
horsepower
Btu/hour
watt
kilowatt (1153)
Since POWER is also the rate at which fuel (energy) is used, how else can it be expressed?
"gallons of oil per hour,
cubic feet of gas per minute, and
tons of coal per day" (1154)
What are the units of electric power?
watt (W)
kilowatt (kW) (1154)
What is the power input in watts to any electrical device having a resistance R and a current I?
W = I^2R = (I) (IR)

(1154)
In dc circuits, because R is not generally known, what is another way to calculate the power input?
W = VI
where
W is watts
R is ohms
I is amperes
V is volts
(1154)
When can you use W = VI with an ac circuit to figure out the wattage of a device?
"In a purely resistive circuit, such as one with only electric heating elements, impedance equals resistance, power factor equals 1.0... it does not matter whether the circuit is ac or dc." (1154)