Final Review Flashcards
A triangle which contains one 90 angle is called a?
Right triangle
A right angle is an angle of
90°
And I right triangle, the longest side is called the
Hypotenuse
The Pythagorean theorem is
C² = a² + b²
A line that indicates both magnitude and direction is a
Vector
Vectors must be adding using using _________addition
Rectangular addition
One method of adding two vectors that originate at the same point is the
Parallelogram method
A device used to change DC into AC is called a
Oscillator
A __________ wave is waveform which zigzags up and down in straight lines
Triangle Wave
A wave in which the voltage rises at a constant rate with respect to time is a?
Linear wave
Rotating machines alternators normally produce a wave shape which is called a?
Sine wave
Alternating current waveforms repeat the same shape over and over from the beginning of one shape to the end of that shape is called
Cycle
The number of cycles complete in one second is called the
Frequency
The unit of frequency is the
Hertz
The value of AC which produces the same amount of heat as DC and load is called the?
RMS value of the AC
Another term used to indicate the same as the RMS value is the?
Effective value
The unit of measure of the power delivered to the load in a DC circuit is?
Watts
I load that will convert all of the delivered power into another form of energy
Resistive load
In an AC circuit, the voltage and current are frequently both sine waves. If they both pass through zero heading in the same direction at the same time they are said to be
In phase
The tendancy for high frequency AC current to travel near the outer part of conductors cause the resistance of these conductors to be higher than on low frequency conducters, this is known as
Skin effect
Current flowing in a conductor and particularly in a coil causes a magnetic field around the conductor or coil The magnetic field in turn induces voltage and current back into the original conductor or coil. That action is caused by characteristics name
Inductance
When current flows in a conductor, a magnetic field is created. The magnetic field cuts the conductor which creates a voltage in the conductor. This voltage is called
Induced voltage
The current limiting property of an inductor is called
Reactance
The unit of inductance is the
Henry
A capacitor is constructed by separating two metal conductors called?
Plates and dielectric
Increasing the surface area of the plates will cause the capacitance of a capacitor to
Increase
In some capacitors there is a small amount of current that flows from one plate through the dielectric material to the other plate. This current is called
Leakage current
In a capacitor the amount of dielectric stress is proportional to
The voltage difference between the plates
In a capacitor the voltage difference between the plates control the
Amount of dielectric stress
Energy in a capacitor is stored as a
Electrostatic charge
The insulating material between the plates is rated by a value called the
Dielectric constant
The unit capacitance is the
Farad
The farad is the unit of
Capacitance
Capacitor charge and discharge at a
Exponential rate
Non-polarized capacitors
Can be used with either AC or DC
Polarized capacitor
Must be used with DC only
Polarized capacitor are also known as
Electrolytic capacitors
Variable capacitor normally have a dielectric of
Air
The JAN standard is used to mark a capacitor intended for
Military
A HIPOT is a test set used to test capacitor
Dielectric
Since a capacitor is two conductor separated by an insulator
DC cannot flow but AC will appear to flow
The capacitive reactants of a capacitor is ________ proportional to the frequency of the applied voltage
Inversely
In an RC parallel circuit, The phase angle between the total voltage and the total current is not 0. The amount of phase angle shifts depends on the ratio of
Watts to volts amperes
In an RC parallel circuit, the voltage across the resistor and the voltage across the capacitor are
In phase
In an RC parallel circuit, the current through the resistor and the current through the capacitor are
Less than 90° out of phase with the resistor current lagging
In a serious RLC circuit, the point at which XL and XC are equal is called
Resonance
The difference between the two frequency at which the current is 0.707 of the maximum is the
Bandwidth
The device needed to convert alternating current to direct current is called?
Rectifier
If a circuit is leading or legging, what two components can be used to reduce the amount of leg or lead?
Capacitor and an inductor
Inductive reactants is caused by the induced voltage and is therefore proportional to three factors that determine induced voltage these factors are
1: Number of turns
2: frequency/speed
3: core material
Three factors that determine the capacitance of a capacitor
1: area of the plates
2: distance between the plates
3: dielectric material
Define lenz law
Induced voltage or current? Oppose a motion that causes it
What is a Henry a measure of?
Inductance
What is inductive reactance?
The equivalent ohmic opposition to current of inductor in an AC circuit
What causes back EMF in an inductor when alternating current is flowing through it?
Opposes current flow
What effect does the inductive reactants have on an AC circuit?
Causes current to leg voltage
What happens to the current in a coil when DC is applied?
Increases over time
What curve explains the way current behaves when DC is applied to a reactor?
Exponential curve
What happens when a coil that is meant to operate on AC is connected to a DC supply?
Current increases and very little resistance
What device can be used to prevent voltage spikes in a DC circuit?
Zener diodes, MOVs, capacitors, flash bulbs
What device can be used to prevent voltage spikes in an AC circuit?
Metal oxidized Varistors (MOVs)
What are some of the advantages of AC over DC?
1-Easy to transform, voltage up and down
2-Easy to make rotating fields for AC motors
3-AC motors are lower maintenance than DC motors
Will 120 volts AC RMS value give the same heating effect as 120 volt DC average value?
Yes
Will 120 volt ACRMS value produce the same amount of heat as 120 true DC will win applied to the same resistor?
Yes
Is true DC equal to average DC
Values are equal
What are the four AC losses?
Skin effect
Eddie currents
Dielectric current
Hysteresis
Do electrical degrees always equal mechanical degrees?
Only on a two-pole generator
Is there any time when electrical degrees will equal mechanical degrees?
Only on a two-pole generator
Does current lead or leg the voltage in inductive circuit?
Leg
Does current lead or leg the voltage in a capacitive circuit?
Lead
What are the three factors that determine the capacitance of a capacitor?
1: The surface area of the plates
2: distance between the plates
3: the electric material between the plates
Will a capacitor be able to store more or less charge if the plates are brought further from each other?
More charge since closer plates with have more capacitance
What is the formula to calculate the charge developed on capacitor plates
C = KxA/ 4.45D
What are the two formulas to calculate the energy stored in a dielectric of a capacitor?
1: Q = CxV
2: Joules =0.5xCxV²
Capacitors in parallel do they add or reciprocal method?
Add
Capacitors in series do they add or reciprocal method?
Reciprocal method
In a parallel circuit, inductance is added?
Inversely
The energy of a capacitor is stored on the plates in the form of a?
Electrostatic or field/charge
Name two common use of a capacitor in AC circuits
AC filters or power factor correction
What two factors determine the capacitive reactants of a capacitor?
Frequency and capacitance
At what time does current flow through a DC series circuit containing a capacitor and when does current stop flowing?
Current flows when it’s charging and discharging. Stops flowing when it’s at full charge
What two tests are used to check a capacitor and what devices are used to perform the test?
Ohmmeter to check is shorted and voltmeter for charge and also a hipot- dielectric strength
Explain in detail what dielectric stress is and what it creates it
Stretching of the orbits of electrons in the dielectric due to the charge on its plates
The quality of a capacitor is found by Q
R/XC
Define Lenz Law?
Induced Voltage or current opposes the motion that causes it.
What is Henry a measure of?
Inductance
What is the definition of Henry? As a coil that inducts 1 volt for every 1 amp/second current change.
What is the definition of inductance?
The ability to produce an opposing voltage into a circuit as a result of changing current.
What is inductive reactants?
An opposition to current in AC, due to alternating current/ field inducing a voltage in an inductor.
What causes back EMF in an inductor when alternating current is flowing through it?
Self-induced. Voltage from the generated field.
What effect does the inductive reactants have on an AC circuit?
Adds impedance, causes current to lag voltage.
What happens to the current in a coil when DC is applied?
Current will ramp up exponentially over time.
What curve explains the way current behaves when DC is applied to a reactor?
Exponential curve.
What happens when a coil that is meant to operate on AC is connected to a DC supply?
A large DC current builds up.
In a DC circuit with a resistor in serious with coil, will it take more time or less time for the current to rise to its full value when we increase the resistance in series with the inductor?
More resistance results in less time until the current is at maximum.
What device can be used to prevent voltage spike in a DC circuit?
Diodes, neon flash bulbs, MOVs, resistors, capacitors
What device can be used to prevent voltage spikes in an AC circuit?
MOV’s (Metal oxide Varistors)
What are some of the advantages of AC over DC?
Easily transformable up and down. More reliable machines.
Will 120 volt AC armrest value give the same heating effect as 120 volt DC average value?
Yes
Well 120 AC RMS value produced the same amount of heat as 120 true DC when applied to the same resistor?
Technically no, since R is higher in AC due to skin effect.
What are the four AC losses?
Skin effect, hysteresis, Eddy currents, dielectric currents.
Do electrical degrees always equal to mechanical degrees?
No. Only in a two pole generator or a motor.
Is there any time when electrical degrees will equal to mechanical degrees?
Yes. In a two pole motor or generator.
What kind of power is produced when current is in phase with voltage?
True power. Active power. Real power.
What kind of power is produced when current is 90° of phase with the voltage?
Reactive power quadrant power.
What kind of power is produced when current is less than 90° with the voltage?
Parent power, VA.
Inductors are said to blank a change in blank.
Inductors are said to oppose a change in current.
