Questions and Answers
The __________ of an AC power source changes periodically.
Polarity
List the three requirements for inducing a voltage.
Conductor, Magnetic field, Relative motion
When a conductor rotating in a magnetic field is cutting through the maximum number of flux lines, what occurs?
Maximum voltage is induced
When a sine wave is used to represent voltage, voltage below the horizontal line is negative.
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The number of cycles completed each second by a given AC voltage is called __________ and is measured in __________.
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The letters used to express effective AC values are __________.
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The physical property of all AC circuits that opposes any change in __________ is called inductance.
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__________ is the measure of the opposition to current flow that is created by inductance.
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When current flowing through a conductor is increasing, what happens?
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When CEMF opposes the applied voltage in an AC circuit, it has the effect of increasing current.
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List two ways to increase inductive reactance in an AC circuit.
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In a purely inductive circuit, __________ is the only current limiting factor.
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Whenever voltage and current increase or decrease at different times, they are said to be __________.
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Capacitance is a physical property of all AC circuits that opposes a change in voltage.
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What is capacitive reactance?
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Capacitive reactance is measured in __________.
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A dielectric in a capacitor:
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Before a capacitor can store energy, it must first be __________.
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When a capacitor is fully charged, the source voltage and the voltage across the capacitor are equal in amount but opposite in polarity.
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Capacitance causes __________ and __________ to be out of phase.
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True power is the amount of power actually used to do work.
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Positive power is power that is:
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Reactive power is power that __________ do useful work.
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The voltage and current sine waves for reactive power are always __________ phase.
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Apparent power is the result of multiplying voltage times current in any circuit.
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The combined effect of resistance, inductance, and capacitance on current flow in an AC circuit is called __________.
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In most cases, true power in AC circuits is calculated with the aid of the __________ associated with the specific circuit.
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The component that changes a two-wire single-phase system into a three-wire single-phase system is a __________.
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The middle line on the secondary side of a three-wire single-phase system is:
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In a three-phase system, the current that flows through the coils or resistors is called __________ current.
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In a delta-connected system, phase voltage equals line voltage, but phase current does not equal line current.
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To calculate the line voltage of a wye-connected three-phase system, multiply the phase voltage by __________.
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In a wye-connected three-phase system, phase current and line current are __________.
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Study Notes
Alternating Current Fundamentals
- Polarity of an AC power source changes periodically.
- Three requirements for inducing a voltage include a conductor, a magnetic field, and relative motion.
- Maximum voltage is induced when a conductor is cutting through the maximum number of magnetic flux lines.
- In a sine wave representation, voltage below the horizontal line is considered negative.
- Frequency measures the number of cycles completed each second, quantified in hertz.
- Effective AC values are expressed using the letters RMS (Root Mean Square).
- Inductance is the property in AC circuits that opposes a change in current flow.
- Inductive reactance measures the opposition to current flow due to inductance.
- An increasing current through a conductor results in a building magnetic field around it.
- Contrary to increasing current, CEMF (counter-electromotive force) opposes the applied voltage, limiting current.
- To enhance inductive reactance in AC circuits: coil the conductor and insert a metal core inside the coiled conductor.
- In a purely inductive circuit, the only current-limiting factor is inductive reactance.
- When voltage and current variations occur at different times, they are described as being out of phase.
- Capacitance is a property that opposes changes in voltage in AC circuits.
- Capacitive reactance measures opposition to current due to capacitance and is quantified in ohms.
- A capacitor's dielectric prevents electron flow between its plates.
- A capacitor must be charged before it can store energy.
- When fully charged, the source voltage equals the voltage across the capacitor in magnitude but opposite in polarity.
- Capacitance creates a phase difference between current and voltage.
- True power is the actual power used to perform work.
- Positive power refers to power supplied to a load from a power source.
- Reactive power does not perform useful work.
- Voltage and current sine waves for reactive power are always out of phase.
- Apparent power results from multiplying voltage times current in any circuit.
- The combined effect of resistance, inductance, and capacitance on current flow in an AC circuit is termed impedance.
- True power in AC circuits is often calculated using the power factor relevant to the circuit.
- A transformer changes a two-wire single-phase system into a three-wire single-phase system.
- In a three-wire single-phase system, the middle line on the secondary side is referred to as the neutral line.
- The current flowing through the coils or resistors in a three-phase system is called phase current.
- In a delta-connected system, phase voltage equals line voltage, but phase current does not equal line current.
- To calculate the line voltage in a wye-connected three-phase system, multiply the phase voltage by 1.73.
- Phase current and line current are equal in a wye-connected three-phase system.
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Test your knowledge of alternating current concepts with these flashcards. Covering key terms like polarity, requirements for inducing voltage, and maximum induced voltage, this resource is perfect for students of electrical engineering. Get ready to strengthen your understanding of AC fundamentals!
