CIE A Level Physics复习笔记21.1.3 Mean Power
Mean Power
- In mains electricity, current and voltage are varying all the time
- This also means the power varies constantly, recall the equations for power:
- Where:
- I = direct current (A)
- V = direct voltage (A)
- R = resistance (Ω)
- The r.m.s values means equations used for direct current and voltage can now be applied to alternating current and voltage
- These are also used to determine an average current or voltage for alternating supplies
- Recall the equation for peak current:
- Therefore, the peak (maximum) power is related to the mean (average) power by:
Therefore, it can be concluded that:
The mean power in a resistive load is half the maximum power for a sinusoidal alternating current or voltage
Mean power is exactly half the maximum power
Worked Example
An alternating voltage supplied across a resistor of 40 Ω has a peak voltage V0 of 240 V.Calculate the mean power of this supply.
Step 1: Write down the known quantities
Resistance, R = 40 Ω
Peak voltage, V0 = 240 V
Step 2: Write out the equation for the peak power and calculate
Step 3: Calculate the mean power
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- The mean power is half of the maximum (peak) power
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Mean power = 1440 / 2 = 720 W
转载自savemyexams
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