Instantaneous Power in AC Circuits Quiz & Flashcards

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Questions and Answers

What is the portion of instantaneous power that results in no net transfer of energy but instead oscillates between the source and load in each cycle due to stored energy?

The portion of instantaneous power that results in no net transfer of energy but instead oscillates between the source and load in each cycle due to stored energy is known as instantaneous reactive power, and its amplitude is the absolute value of reactive power.

Explain the concept of instantaneous active power in an alternating current circuit.

Instantaneous active power refers to the portion of instantaneous power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction. Its time average is known as active power or real power.

In a simple AC circuit with a purely resistive load, what is the nature of the instantaneous power?

In a simple AC circuit with a purely resistive load, the instantaneous power, given by the product of voltage and current, is always positive, such that the direction of energy flow does not reverse and always is toward the resistor. In this case, only active power is transferred.

If the load in an AC circuit is purely reactive, what is the phase relationship between the voltage and current?

If the load in an AC circuit is purely reactive, then the voltage and current are 90 degrees out of phase. Signup and view all the answers

What are the SI units of instantaneous power in an electric circuit?

The SI unit of instantaneous power in an electric circuit is the watt. Signup and view all the answers

What is power factor and how does it relate to active, reactive, and apparent power?

Power factor is a measure of how effectively electrical power is being used. It is the ratio of real power (kW) to apparent power (kVA). Active power (kW) is the useful power, reactive power (kVAR) is the wasted power, and apparent power (kVA) is the demand power. Signup and view all the answers

How does a circuit's efficiency relate to its demand and supply power, and what challenges does high demand pose to utilities?

In a 100% efficient circuit, demand would be equal to the power available. High demand places a strain on the utility system, leading many utilities to add demand charges to offset differences between supply and demand. Utilities face the challenge of delivering power to handle every customer’s peaks, especially during peak demand. Signup and view all the answers

Why do many utilities add a demand charge to the bills of large customers, and how is demand calculated based on load requirements?

Many utilities add a demand charge to offset differences between supply and demand. Demand is calculated based on the average load placed within 15 to 30 minutes. Irregular demand requirements necessitate more reserve capacity for utilities. Signup and view all the answers

What is peak demand, and why is it a challenge for utilities to handle every customer's peaks?

Peak demand is when demand is at its highest. Utilities face the challenge of delivering power to handle every customer’s peaks, which can disrupt overall supply unless there are enough reserves. Signup and view all the answers

Explain the relationship between power factor and utility billing, and why using power at the very moment it is in highest demand can disrupt overall supply.

Utilities bill for peak demand, and using power at the very moment it is in highest demand can disrupt overall supply unless there are enough reserves. This is why many utilities add a demand charge to offset differences between supply and demand. Signup and view all the answers

Study Notes

Power in AC Circuits

The portion of instantaneous power that results in no net transfer of energy but instead oscillates between the source and load in each cycle is known as reactive power.
Instantaneous active power in an alternating current (AC) circuit is the rate at which energy is transferred from the source to the load.

Instantaneous Power in Simple AC Circuits

In a simple AC circuit with a purely resistive load, the instantaneous power is always positive, indicating that energy is being transferred from the source to the load.

Purely Reactive Loads

If the load in an AC circuit is purely reactive, the phase relationship between the voltage and current is 90 degrees, meaning the voltage and current are out of phase.

Units of Instantaneous Power

The SI units of instantaneous power in an electric circuit are watts (W).

Power Factor and Apparent Power

Power factor is the ratio of active power to apparent power, and it relates to active, reactive, and apparent power.
Active power is the actual power used by a load, apparent power is the vector sum of active and reactive power, and reactive power is the portion of power that does no useful work.

Circuit Efficiency and Utility Challenges

A circuit's efficiency is related to its demand and supply power, with high demand posing challenges to utilities.
High demand can lead to brownouts or blackouts if utilities cannot supply enough power to meet the demand.

Demand Charges and Peak Demand

Utilities add a demand charge to the bills of large customers to encourage them to reduce their peak demand.
Demand is calculated based on load requirements, and peak demand is the highest amount of power required by a customer over a given period.
Peak demand is a challenge for utilities because it requires them to have excess capacity available to meet the high demand.

Power Factor and Utility Billing

Power factor affects utility billing because a low power factor indicates that a customer is using more reactive power, which can strain the utility's system.
Using power at the moment of highest demand can disrupt the overall supply, leading to power quality issues and increased costs for utilities.

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Description

Test your knowledge of instantaneous power in alternating current circuits with this quiz. Explore the concepts of energy flow, inductors, capacitors, and the SI unit of power.

Instantaneous Power in AC Circuits Quiz