Edison Study
When resistors are placed in parallel across a voltage source, the voltage is ____ across each resistor.
Equal
To solve a series parallel circuit, reduce the compound circuits to ____ simple circuits.
Equivalent
All magnets have two characteristics. They attract and hold ___. If free to move, like the compass needle, the magnet will assume roughly a ____ position.
Iron, north-to-south
In unequal resistors formula in a parallel, after adding the resistors, you need to ____ both sides of the equation to solve it.
Invert
Current in a parallel circuit. Total current in a parallel circuit is equal to the sum of the current in each branch. Equation:
It = I1 + I2 + I3
This formula applies to current in a parallel circuit.
It = I1 + I2 + I3
The sum of the voltage drops across the resistances of a closed circuit equals the total voltage applied to the circuit.
Kirchhoff's law
Inductance is designated by the letter "___" and the unit of measurement for inductance is ____.
L, Henry (h)
1 kiloampere. Symbol & decimal.
1 kA, 1000 A
1 milliampere. Symbol & decimal.
1 mA, 1/1000 A
Megohm = ____.
1,000,000 ohms
Electrons in the outer band are ____ displaced by application of an external force.
Easily
The _____ of voltage and current is the common method of expressing the value of AC.
Effective value
An _______ field is a magnetic field generated by current flow in a conductor.
Electromagnetic
_____ states that electrons flow from negative to positive.
Electron flow concept
Apparent power is power in an AC circuit is the vector sum of true power and reactive power.
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Basic generator operation: an armature rotates through the magnetic field. At an initial position of zero degrees, the armature conductors are moving parallel to the magnetic field and not cutting through any magnetic lines of flux. No voltage is induced.
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Capacitors usually are rated in microfarads or picofarads.
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If voltage were read across a combination of R3 and R4, meter would read six volts. For R2, R3, and R4 volts would be nine. Continued.
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Mutual induction is the coupling of inductances by their mutual magnetic fields.
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Phase relationship between current and voltage in an inductive circuit. Current does not rise at the same time as the source voltage in an inductive circuit. In a purely resistive circuit, current and voltage rise and fall at the same time.
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Power factor is the ratio of true power to apparent power in an AC circuit
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Simple inductive circuit. In a resistive circuit, current change is considered instantaneous. If an inductor is used, the current does not change as quickly.
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The rating for electrical equipment is an indication of the rate at which the equipment converts electrical energy into other forms of energy, such as heat or light.
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Three-phase transformers are used when three phase power is required for larger loads such as industrial motors.
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True power is power consumed by a resistor is dissipated in heat and not returned to the source.
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The total current of s simple circuit with a voltage supply of 12 volts and a resistance of 24 ohms is ____ amps.
.5 amps
1 microampere. Symbol & decimal.
1 "upside down n w/ line down", 1/1,000,000 A
Formula for total inductance for parallel inductors.
1/Lt = 1/L1 + 1/L2 + 1/L3
Formula used when there are three or more resistors.
1/Rt = 1/R1 + 1/R2 + 1/R3
If a 4 ohms resistor is placed in series with a 6 ohms resistor, the total value would be ____.
10 ohms
Kilo = ____. Milli = ____. Micro = _____.
1000, 1/1000, 1/1,000,000
In exponential form, how many atoms does it take to fill one cubic centimeter of s copper conductor?
10^24
Each phase of three phase AC power is offset by ____ degrees.
120 electrical
A common household lamp may be rated for ___ volts and ___ watts.
120,100
What is the total current of a series circuit that has a 120 volt supply and a 60 ohms resistance.
2 amps
When voltage supplied is 10V and resistance is 5 ohms, what is the current?
2 amps. (I = 10 volts/5 ohms)
If the ammeter reads 200 mA and resistance is known to be 10 ohms, what is the voltage?
2 volts. (E =.2 x 10)
Current is determined by the number of ____ that pass through a cross section of a conductor in one second.
Electrons
If the armature rotates at a speed of 60 revolutions per second, the generator voltage will be ___ cycles per second.
60
In the U.S., alternating current is usually generated at ___ hertz.
60
A time constant is the time, in seconds, requires for the circuit current to rise to ___ of its maximum value.
63.2%
Elements are identified by the number of _____ in orbit around the nucleus.
Electrons
Inductance is usually indicated symbolically on an electrical drawing one of two two ways.
A curled line or a filled rectangle
Instantaneous voltage is ____ to to the peak voltage times the sine of the angle of the generator armature.
Equal
Another name for an AC generator is an _____.
Alternator
Current is always expressed in _____ or ____.
Amperes, amps
Current is measured in ____ which is abbreviated ____. The symbol is ___.
Amperes, amps, A
Resistance is usually indicated symbolically on an electrical drawing by one of two ways.
An unfilled rectangle or a zig-zag line.
An ____ is any number of conductive wires wound in loops which rotates through the magnetic field.
Armature
The basis of electricity is _____.
As free electrons move from one atom to the next an electron flow is produced.
Two unlike poles brought together cause the magnets to ____ each other. Two like poles brought together cause the magnets to ___ each other.
Attract, repel
DC power sources include ____ and ____.
Batteries and DC generators
Electrons bound in their orbit by the attraction of protons.
Bound electrons
The ____ of a capacitor depends on the area of the plates, the distance between the plates, and the material of the dielectric.
Capacitance
_____ is a measure of a circuit's ability to store an electrical charge.
Capacitance
A device manufactured to have a specific amount of capacitance is called a _____.
Capacitor
____ ride against the slip rings to conduct a current from the armature to a resistive load.
Carbon brushes
Alternating voltage and current are constantly ____ values.
Changing
Series-parallel circuits are also known as ____.
Compound circuits
Good conductors are _____.
Copper, silver, aluminum, zinc, brass, and iron.
When equal resistances are placed in a parallel circuit, opposition to current flow is ____ in each branch.
Equal
The force of attraction or repulsion depends on strength of the charged bodies, and the distance between them.
Coulomb's Law of Charges
Ammeter measures what?
Current flowing in the circuit.
The flow of electrons is referred to as ____ and is designated by the symbol ___.
Current, I
George Simon Ohm. Ohm formulated a law which states that ____ varies directly with ____ and inversely with ____.
Current, Voltage, resistance,
The supply of current for electrical devices may come from a ___ source, or an ___ source.
DC, AC
Another name for the insulating material in a capacitor is ____ material.
Dielectric
When unequal value resistors are placed in a parallel circuit, opposition to current flow is ____ in every circuit branch.
Different
If current increases, inductance tries to hold it ____. If current decreases, inductance tries to hold it ___.
Down, up
Solve for voltage across any resistor: (E = I x R, E = 2 x 1.5)
E = 3 volts
Voltage is designated by these two symbols.
E or V
The easy triangle diagram of Ohm's law has ___ on top of __ and ___.
E, I and R. Or E = I x R
All voltage sources share the characteristic of an ____ of electrons at one terminal and a ____ at the other terminal. This results in a difference of potential between the two terminals.
Excess, shortage
The unit of measurement for capacitance is ____, abbreviated __.
Farads, F
A 100 watt lamp converts energy ___ than the 75 watt lamp.
Faster
It takes about ___ time constants for current to reach its maximum value.
Five
An electron forced out of orbit by an external force is called a ______.
Free electron
The number of cycles per second made by voltage induced in the armature is the ____ of the generator.
Frequency
Current is ____ through the path of least resistance.
Greater
The accepted term for cycles per second is ____.
Hertz
The unit of measurement of cycles per second is ____.
Hertz
Ohms symbol is __.
Horse-shoe
The three most common forms of magnets are the ____, ____, and _____.
Horse-shoe, bar and compass needle
Solve current when Rt = 6 and voltage is 12. (I = E/R)
I = 2 amps
When E-in is 50 volts, and Rt is 25 ohms (R1 being 5 and R2 being 20), solve for current and E-out. (I = E-in/Rt, E-out = I x R2)
I = 2 amps, E-out = 40 volts
The three mathematical ways to express Ohm's law are ____.
I = E/R, E = I x R, or R = E/I
Calculate restive current.
I = E/Z
Current flow with unequal value resistors in a parallel circuit: using ohm's law, use this formula to calculate total current for each circuit.
I1 = E/R1, I2 = E/R2, It = I1 + I2
With unequal value resistors in a parallel circuit. Use this formula to find total current.
I1 = E/R1, I2 = E/R2, It = I1 + I2
Total opposition to current flow in an AC circuit that contains both reactance and resistance is called _____. Designated by the symbol ___.
Impedance, Z
An increase in the number of poles would cause an ____ in the number of cycles completed in a revolution.
Increase
With an increase of length or a decrease of cross-section of a conductor, resistance will ____.
Increase
As current flow increases, field strength ____, and as current flow decreases, field strength ____.
Increases, decreases
Current is constantly changing in AC, so ____ is a continual factor.
Inductance
_____ is the property of an electric circuit that opposes any ____ in electric current.
Inductance, change
Inductance in an AC circuit causes a continual opposition. This opposition to current flow is called _____ and is designated by the symbol X-L.
Inductive reactance
Inductance is somewhat like mechanical _____.
Inertia
The _____ is the value at any one particular time. It can be in the range of anywhere from zero to the peak value.
Instantaneous value
In the equation e = E-peak x sin-o, e is:
Instantaneous voltage
If a current-carrying conductor is grasped with the left hand with the thumb pointing in the direction of electron flow, the fingers will point in the direction of the magnetic lines of flux.
Left-hand rule for conductors
Small values of resistance means ____ opposition to current flow.
Less
Invisible magnetic _______ leave the North Pole and enter the South Pole. While they are invisible, the effects of magnetic fields can be made visible.
Lines of flux
The electric field around a charged body is represented by invisible ________.
Lines of force
It is often desirable to use a voltage potential that is ____ than the supply voltage.
Lower
Total inductance is calculated using the following formula.
Lt = L1 + L2 + L3
An electromagnet can be made to control the strength of its field which controls the stength of the _____.
Magnetic poles
The principles of ____ are an intregal part of electricity.
Magnetism
Conductors allow ____ free electrons to flow when an external force is applied.
Many
Semiconductor devices can be manufactured to allow ____ electrons to flow in one direction and _____ electrons to flow in the opposite direction.
Many, few
Every magnet has two poles, one north and one south. This is the point at which ____ attraction occurs.
Maximum
A large variety of electrical devices such as ___, ____, ____, ____ and ____ use electromagnetic principles.
Motors, circuit breakers, contactors, relays, and motor starters
A material that has an excess of electrons is said to have a ____ charge. One with a deficiency is said to have a ____ charge.
Negative, positive
In AC, electrons will flow through a conductor from the ____ terminal to the ____ terminal, first in one direction then another.
Negative, positive
The left hand rule for coils: the fingers of the left hand are wrapped around the coil in the direction of electron flow and the thumb points to the ___ pole of the coil.
North
Reactance and impedance is expressed in ____.
Ohms
Resistance is always expressed in ____.
Ohms
A sine wave moves through a complete rotation of 360 degrees, which is referred to as _____.
One cycle
A two pole generator would complete ____ cycle per revolution and a four-pole generator would complete ___ cycles per revolution.
One, two
Power consumed in a resistor depends on the amount of current that passes through the resistor for a given voltage. This is expressed as voltage times current.
P = E x I or P = EI
Power can also be calculated by substituting other compounds of Ohm's law.
P = I^2 x R and P = E^2/R
An AC generator produces one cycle per revolution for each ____.
Pair of poles
A _____ is formed when two or more resistances are placed in a circuit side-by-side so that current can flow through more than one path.
Parallel circuit
The _____ of a sine wave occurs twice each cycle, once at the positive maximum value and once at the negative maximum value.
Peak value
The value of the voltage or current between the peak positive and peak negative values is called the _____.
Peak-to-peak value
Good insulators are ____.
Plastic, rubber, glass, ceramics.
In AC sine wave, when the waveform is above the time axis, current is flowing in one direction and is referred to as the ____ direction. When it's below the time axis, current is flowing in the opposite direction and known as the ___ direction.
Positive, negative
On a battery, the longer line indicates the ____ terminal. The shorter line indicates the ____ negative.
Positive, negative
The rate at which work is done is called ____ and is represented by the symbol __.
Power, P
In direct current electricity, electrons flow continuously in one direction from the source of ___ through a conductor to a ___ and back to the source of ___.
Power, load, power
For a lamp with 120 volts and 100 watts, find value of resistance. (P = E^2/R which can be transposed to R = E^2/P)
R = 120^2/100, R = 144 ohms
Simplifying a series-parallel circuit to a parallel circuit. Simplify R1 and R2.
R = R1 + R2
Formula to determine total resistance of a parallel circuit to find the total resistance of R1 and R2.
R = value of any one resistor/number of resistors
Resistance is designated by the symbol ___. The unit of measurement for resistance is ____.
R, ohms
Effective value is also known as the ____ value.
RMS (root-mean-square)
In an AC circuit containing only inductance, capacitance, or both, opposition to current flow is called ____.
Reactance
Like charges ____ and unlike charges _____.
Repel, attract
AC is divided into single-phase and three-phase types. Single phase is used for small electrical demands, such as _____. Three phase is used where large blocks of power are required, such as found in _____.
Residential homes, commercial buildings
____ opposes current flow, ____opposes change in current flow.
Resistance, inductance
A basic generator consists of magnetic field, an armature, slip rings, brushes and a _____.
Resistive load
A series circuit where R1 is 11K ohms, R2 is 2K ohms, R3 is 2K ohms, R4 is 100 ohms, and R5 is 1K ohms, what is the total resistance?
Rt (resistance total) = 16,100 ohms
In a parallel circuit with two resistors, R1 being 5 and R2 being 10, find Rt.
Rt = 3 1/3 or 3.33
When 3 resistors all are 15 ohms, what is Rt?
Rt = 5 ohms
The mathematical formula for resistance in series:
Rt = R1 + R2 + R3 + R4
Formula when there are only two resistors. (Parallel circuit)
Rt = R1 x R2 / R1 + R2
Total current can also be calculated by first calculating total resistance, then applying the formula for Ohm's Law.
Rt = R1 x R2/R1 + R2, then It = E /Rt
To determine Rt when resistors are of equal value in a parallel circuit, use this formula.
Rt = Value of any one resistor/number of resistors
When equal resistances are placed in a parallel circuit, opposition to current flow is the ____ in each branch.
Same
A change in the magnetic field surrounding the conductor induces a voltage in the conductor. This _____ voltage opposes the change in the current and is known as ____.
Self-induced, counter emf
A ____ is formed when any number of resistors are connected end-to-end so that there is only one path for current to flow.
Series circuit
The ____ illustrates how voltage and current in an AC circuit rises and falls with time.
Sine wave
The graphic representation of AC voltage and current values over a period of time is a _____.
Sine wave
The time constant is designated by the symbol ___.
Small "T"
Capacitance is usually indicates symbolically on an electrical drawing by a combination of a straight line with a curved line, or two _____ lines.
Straight
If L1 is equal to 15 millihenrys, and R1 is equal to 5 Ohm's, find time constant.
T = 3 milliseconds
To determine the time constant of an inductive circuit use one of these formulas.
T(in seconds) = L/R, T(in milliseconds) = L(millihenrys)/R, T(in microseconds) = L(microhenrys)/R
Calculating the time constant of a capacitive circuit. Formula:
T(seconds) = R(megohms) x C(microfarads), T(microseconds) = R(megohms) x C(picofarads), T(microseconds) = R(Ohms) x C(microfarads)
The AC generator reverses _____ many times a second.
Terminal polarity
Voltmeter measures ____.
The value of voltage supplied.
AC sine wave. A sine wave can represent current or voltage. There are two axes. The vertical axis represents the direction and magnitude of current or voltage. The horizontal axis represents ___.
Time
The time required for the current to rise to its maximum value is determined by the ratio of inductance, in Henry's, to resistance, in ohms. This ratio is called the ____ of the inductive circuit.
Time constant
Examples of inductors are ___, ___ and ____.
Transformers, chokes, motors
The principle of semi-conductors is the basis for ____, _____, and other ______.
Transistors, diodes, solid-state electronic devices.
In a current carrying coil, the strength of the field can be increased by adding more ___ to the coil or by increasing the ____.
Turns, current
The inductance of a coil is determined by the number of ____ in the coil, the ____ between the turns, the coil ___, the core material, the number of layers of windings, the type of winding, and the ___ of the coil.
Turns, spacing, diameter, shape
The frequency is the same as the number of rotations per second if the magnetic field is produced by only ____.
Two poles
A ____ is a graphic representation of a quantity that has direction and magnitude.
Vector
The force that is applied to a conductor to cause current flow is ____.
Voltage
To get the desired voltage potential which is lower, a ____ can be used.
Voltage divider
The voltage across a resistor is referred to as _____.
Voltage drop
A simple electric circuit consists of a ____ source, some type of ____, and a ____ to allow electrons to flow between the two.
Voltage, load, conductor
Ohms law. Current = _____.
Voltage/resistance or I = E/R
The unit of measurement for voltage is ____ which is designated by the letter "__"
Volts, V or E
Voltage is always expressed in ___.
Volts, or V, E
The ___ is defined as the rate work is done in a circuit when 1 amp flows with 1 volt applied.
Watt
Electrical equipment is rated in ____.
Watts
Power is measured in ____ and is represented by the symbol __.
Watts, W
The formula for inductive reactance is
X-l = 2pie x fl, or X-l = 2 x 3.14 x frequency x inductance
Capacitive reactance is designated by the symbol ___.
Xc
The following formula can be used to calculate capacitive reactance.
Xc = 1/2pie x f x C
For an inductive circuit, ohm's law can be used to find total circuit current.
Z = square of R^2 + inductive reaction (X-l)^2
The following formula is used to calculate impedance in an inductive circuit.
Z = square root of R2 + X-l^2
What is the instantaneous voltage at 240 degrees for a peak voltage of 150 volts?
e = -.866 x 150
Sin 0 = sine of the angle . The sine curve represents a graph of this equation.
e = E-peak x sin-o
