Questions and Answers
What is the formula for electric power in relation to energy consumption and time?
Which of the following formulas can be used to calculate electric power?
What do you multiply single phase power by when using line to line voltage in three phase AC power?
√3
What is real power used for in AC circuits?
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What does reactive power represent in AC circuits?
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What is the formula for apparent power in AC circuits?
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What is the relationship between real power, reactive power, and apparent power?
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Study Notes
Electric Power Basics
- Electric power (P) is calculated as ( P = \frac{E}{t} ), where E is energy in joules (J) and t is time in seconds (s).
- Power is measured in watts (W).
Key Electric Power Formulas
- Alternative formulas for electric power include:
- ( P = V \cdot I ) (Voltage multiplied by Current)
- ( P = I^2 \cdot R ) (Current squared multiplied by Resistance)
- ( P = \frac{V^2}{R} ) (Voltage squared divided by Resistance)
- Symbols represent:
- V = Voltage in volts (V)
- I = Current in amps (A)
- R = Resistance in ohms (Ω)
AC Circuits Power
- Single-phase AC power can transition to three-phase AC power:
- When using line-to-line voltage (( V_{L-L} )), multiply by ( \sqrt{3} ) (approximately 1.73) for power calculations.
- When using line-to-zero voltage (( V_{L-0} )), multiply by 3.
Real Power in AC Circuits
- Real power (P) signifies usable power to perform work on the load and is given by:
- ( P = V_{rms} \cdot I_{rms} \cdot \cos \phi )
- Definitions include:
- ( V_{rms} = \frac{V_{peak}}{\sqrt{2}} ) (Root mean square voltage)
- ( I_{rms} = \frac{I_{peak}}{\sqrt{2}} ) (Root mean square current)
- ( \phi ) represents the phase angle (difference between voltage and current).
Reactive Power in AC Circuits
- Reactive power (Q) denotes power that does not perform useful work, described by:
- ( Q = V_{rms} \cdot I_{rms} \cdot \sin \phi )
- Reactive power is measured in volt-ampere-reactive (VAR).
Apparent Power in AC Circuits
- Apparent power (S) indicates total power supplied to the circuit, calculated as:
- ( S = V_{rms} \cdot I_{rms} )
- Measured in volt-amperes (VA).
Power Relations in AC Circuits
- The relationship among real power (P), reactive power (Q), and apparent power (S) is given by:
- ( P^2 + Q^2 = S^2 )
- This relationship highlights that real and reactive power combine to form apparent power.
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Test your knowledge on electric power equations with these flashcards. Each card presents key formulas and definitions to help you understand the relationship between voltage, current, and power. Perfect for students studying electricity and physics.
