Mike Holt exam prep unit 3 practice questions
In a purely inductive reactive circuit, the self-induced voltage waveform (CEMF) is _____ out-of-phase with the current waveform and 180° out-of-phase with the applied voltage waveform. 45° 90° 120° 180°
90°
"_____" is the ability of a device to store electrical energy and to release that energy. Inductance Resistance Capacitance Capacity
Capacitance
For alternating current, the effective value can be determined by using which of the following formulas? Effective Value = RMS Value Effective Value = Peak Value x 0.707 Effective Value = Peak Value/1.414 all of these
Effective Value = RMS Value Effective Value = Peak Value x 0.707 Effective Value = Peak Value/1.414 all of these
A simple ac generator can be visualized as a loop of wire rotating within the magnetic lines of force between similar poles of a magnet. True False
False
The peak value of a waveform is the maximum value the current or voltage waveform reaches during each full cycle of the rotation of the generator's rotor. True False
False
A "lagging" waveform is when the voltage lags behind the current and a "leading" waveform means the voltage leads the current. True False
True
A pure direct-current waveform displays the polarity and magnitude of the current or voltage as a flat waveform. True False
True
A three-phase generator has each of its three windings evenly spaced around the rotor and the windings are 120° out-of-phase from each other. True False
True
Capacitors are often used to smooth out pulsating direct-current waveforms when ac is rectified to dc. True False
True
Power factor is a measurement of how far the current waveform is out-of-phase with the voltage waveform. True False
True
Waveforms that are "in-phase" with each other means that at every instant, the current is exactly in step with the applied voltage, and both the current and voltage waveforms reach their zero and peak values at the same instant in time. True False
True
When a magnetic field moves through a coil of wire, the lines of force of the magnetic field cause electrons in the wire to flow in a specific direction. When the magnetic field moves in the opposite direction, electrons in the wire flow in the opposite direction. True False
True
In circuits with _____ loads, the voltage waveform finishes after the current waveform so the voltage "lags" the current. linear inductive resistive capacitive
capacitive
When a _____ has reached its maximum potential difference between its metal plates, it's said to be "charged." transistor diode rectifier capacitor
capacitor
A wire's resistance is inversely proportional to its length. True False
false
When the term "_____" is used in relation to waveforms, it indicates the degree relationship between two waveforms, such as voltage-to-current or voltage-to-voltage. lead sync phase lag
phase
A _____ load has its voltage waveform finishing its cycle at the same time (without lead or lag) as the current waveform. linear nonlinear resistive capacitive
resistive
The most significant use of self-induction for industry includes _____. transformers motors generators all of these
transformers motors generators all of these
A self-induced voltage waveform, also known as counter-electromotive force (CEMF), is _____ out-of-phase with the applied voltage waveform. 45° 90° 120° 180°
180°
The formula used for efficiency calculations is _____. Efficiency = Output Watts/Input Watts Input Watts = Output Watts/Efficiency Output Watts = Input Watts x Efficiency any of these
Efficiency = Output Watts/Input Watts Input Watts = Output Watts/Efficiency Output Watts = Input Watts x Efficiency any of these
Another use for a capacitor is starting single-phase motors. A "start" capacitor is connected to the rotor circuit to create the initial electromagnetic field for the rotor to begin moving. True False
True
As the frequency at which electromagnetic fields expand and collapse increases, the self-induced voltage within the wire increases. True False
True
Capacitors are also used to store arc producing energy spikes caused by circuit inductance when switch or relay contacts open under load. True False
True
Current flow in an alternating-current circuit moves in both directions due to the changing polarity of the voltage, whereas direct current flows only in one direction. True False
True
Depending on the instant selected, the instantaneous value can range anywhere from a zero, to a positive peak, or to a negative peak. True False
True
Effective current value is also known as the "Root-Mean-Square" (RMS) value. True False
True
Efficiency describes how much input energy in watts is used for its intended useful purpose and is expressed as a ratio of output power to input power. True False
True
For a pure resistive load, there's no leading or lagging of the voltage relative to the current. The power factor of the circuit is 100 percent or "Unity." True False
True
For current to flow through a circuit, the power source must apply enough electromotive force (voltage) to cause electrons to flow. True False
True
Frequency is expressed as cycles per second, or Hertz (Hz). True False
True
If a capacitor becomes overcharged, the electrons from the negative metal plate can be pulled through the insulation (dielectric) to the positive metal plate by an excessive electric field. True False
True
Root-Mean-Square (RMS) describes the calculation steps (in reverse) necessary to determine the effective ac voltage or ac current value of a waveform. True False
True
The Formula Wheel is a combination and expansion of the Ohm's Law Formula Circle and Watt's Law. True False
True
The Power Formula Circle ("Watt's Law") demonstrates the relationship between power, current, and voltage. Watt's Law states that power is equal to current x voltage. True False
True
The effective value of ac voltage or ac current is the equivalent value of dc voltage or dc current that would produce the same amount of heat in a resistor. True False
True
The heating of wires, transformers, and motor windings is wasted energy and is called "power losses." True False
True
The only thing needed to induce voltage is relative motion between a wire and an electromagnetic field and is the principle that explains how generators and transformers function. True False
True
The power factor of inductive loads causes the VA load to be greater than the true power (watts). True False
True
The resistance in a wire is inversely proportional to its cross-sectional area. If the wire's diameter is increased, then its resistance will decrease. True False
True
The total power consumed in a parallel circuit equals the sum of the powers in each branch. True False
True
The waveform for alternating-current circuits is symmetrical with positive above and negative below the zero-reference level. True False
True
True power is always equal to, or less than, apparent power (VA) and is expressed in watts. True False
True
Voltage induced in a wire by its own expanding and collapsing electromagnetic field is known as "self-induced voltage." True False
True
When alternating current is applied to a capacitor, the current continuously moves back and forth charging and discharging the capacitor. True False
True
To discharge a capacitor, a _____ path is required between its positive (+) and negative ( grounded resistive conductive inductive
conductive
The amount of self-induced voltage created within a winding is directly proportional to _____. current flow the number of wire loops (or turns) frequency at which the expanding and collapsing electromagnetic fields cut through the wires of the winding all of these
current flow the number of wire loops (or turns) frequency at which the expanding and collapsing electromagnetic fields cut through the wires of the winding all of these
A waveform is a mathematical representation on a graph that can be used to visualize the level and direction of _____ in a circuit. current or resistance wattage or voltage current or voltage current or wattage
current or voltage
Capacitance is measured in units of _____. joules farads volts watts
farads
In circuits with _____ loads, the voltage waveform finishes its cycle before the current waveform, so the voltage waveform "leads" the current waveform. linear nonlinear resistive inductive
inductive
The electromagnetic field intensity of a coil of wires (winding) carrying alternating current can be increased by inserting a soft _____ core within the wire winding. aluminum copper iron lead
iron
A nonsinusoidal (or nonsymmetrical) waveform is produced when multiple alternating-current waveforms of different frequencies are introduced on a circuit, typically by _____. short circuits ground faults nonlinear loads overloads
nonlinear loads
The voltage produced by an ac generator is dependent upon the _____. number of turns of wire strength of the magnetic field speed of rotation of the coil all of these
number of turns of wire strength of the magnetic field speed of rotation of the coil all of these
Eddy currents are small independent currents near the center of a wire that are a result of _____ from the expanding and collapsing electromagnetic field. mutual induction over heating self-induction overcurrent
self-induction
The _____ the metal plates is(are) factor(s) in determining capacitance. surface area of distance between insulating material (or dielectric) between all of these
surface area of distance between insulating material (or dielectric) between all of these
When describing the relationship between voltage and current waveforms, the reference waveform (the one used to compare against) is the _____. current resistance voltage wattage
voltage
Power is the rate at which electrical energy is transferred by an electric circuit in a given amount of time at a steady rate and is measured in _____. amperes watts volts hertz
watts
True power is the total energy consumed and is expressed in _____. volt-amperes (VA) watts (P) current (I) resistance (R)
watts (P)
Most commercial alternating-current power is produced by a generator driven by _____. wind steam water any of these
wind steam water any of these
When a wire is coiled into adjacent loops (helically wound), it's called a(an) _____. rotor induction coil capacitive coil winding
winding
