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OmegaFury
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Homework Statement
The resistance of the armature windings of a DC motor is 5Ω. The motor is connected to a 120V line. When the motor is spinning at full speed, it draws a current of 4A. The back EMF at full speed is:
Homework Equations
Pav=[itex]\frac{1}{2}[/itex]I2peakR
Pav=[itex]\frac{1}{2}[/itex]εpeakIpeak
The Attempt at a Solution
Pav=[itex]\frac{1}{2}[/itex]I2peakR
=[itex]\frac{1}{2}[/itex](4A)25Ω=40W
Pav=[itex]\frac{1}{2}[/itex]εpeakIpeak
2Pav/Ipeak=εpeak
2(40W)/4A=20V.
This isn't correct. I also didn't know what to do with the 120V line.