A voltage that changes with time. Peak and rms values, an AC voltage across a resistor, an inductor and a capacitor, reactance, and phasors that show the phase between voltage and current.
3 lessons, about 1 h 45 min3 simulations11 problems6 practice questionsPython in every lesson
Created by StemPy LabAn alternating voltage swings between positive and negative, , with . Across a resistor the current has the same shape and is in phase with the voltage. The average of the current is zero, so we use the rms value, , which heats a resistor as much as a steady current of the same size.
A coil in an AC circuit opposes the current by its reactance , and its current lags the voltage by . A capacitor opposes it by , and its current leads the voltage by . Neither one uses power on average: they store energy and give it back.
A phasor is an arrow that turns at the angular frequency . Its vertical part is the voltage or the current at that instant, and the angle between two phasors is the phase difference. A phase of is a time delay . Phasors are added like arrows. Reactance depends on frequency, unlike resistance.
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