Efficiency
The share of input energy or power that becomes the intended useful output, usually written as a percentage. Losses such as heat mean a real or motor delivers less useful power than it takes in. Efficiency compares input with output; it is different from , which compares real and apparent power in an circuit.
Using Efficiency in context
Updated
A distinction worth remembering
Efficiency compares useful output with input on the same basis. Power factor concerns a different relationship, so a high power factor is not proof of high efficiency.
Questions to take further
- How can I revise Efficiency beyond the definition?
- Explain what Efficiency describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Open University: relationships between electrical quantities — The relationship between voltage, current and resistance and the limits of an ohmic model.
Where Efficiency fits in the learning path
The Electrical Science section covers these units:
- Circuit Fundamentals
Curriculum mapping: C&G 2365 Units 202/302.
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1. Read it in context
- Ohm's LawElectrical Science
- Three-Phase PowerElectrical Science
2. Try recalling, then explore practice
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- Electrical Science — quiz previewFree · Electrical Science
3. Return to the meaning
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Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
Electrical energy is the amount transferred over time, measured in joules (J) or, on electricity bills, kilowatt-hours (kWh). A load drawing a steady 1 kW for two hours uses 2 kWh. Power describes the rate of transfer; energy describes the accumulated amount. A battery capacity quoted in kWh is therefore different from its power rating in kW.
Electrical energy
Read the Electrical energy entryCompare related terms
Open a meaning to compare its role with Efficiency, or follow its full entry.
Electrical energy
Electrical energy is the amount transferred over time, measured in joules (J) or, on electricity bills, kilowatt-hours (kWh). A load drawing a steady 1 kW for two hours uses 2 kWh. Power describes the rate of transfer; energy describes the accumulated amount. A battery capacity quoted in kWh is therefore different from its power rating in kW.
Read the Electrical energy entryElectrical power
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Read the Electrical power entryPower factor
The ratio of real power to apparent power in an AC circuit. Phase displacement and waveform distortion can affect it. Real power includes power dissipated as losses as well as useful output, so power factor is different from efficiency. A lower power factor means more RMS current is needed for the same real power at the same RMS voltage.
Read the Power factor entryA definition is a start. Using it in a real question is where it sticks.