Why doesn't current cancel in a generator?

I am a little confused about the application of Faraday's law in a generator. If we imagine a magnet attached to a wheel (which spins when water falls on it) next to a coil, as the magnet spins around, current will be generated due to electromagnetic induction. However, when we measure the current, the needle on the galvanometer swings back and forth. Why doesn't the current cancel out when it goes from positive to negative on the galvanometer?

• What do you mean, "cancel out?" I have to assume that when you say, "coil," you must be talking about a closed loop because if the loop were not closed, then no current could flow. If you integrate the current over time, that should give you the total amount of charge that has moved past a given point, and if the integration is over exactly one turn of the wheel, that value should be zero. Is that what you mean by "cancel out?" – Solomon Slow Jul 27 at 17:21
• Maybe what you are asking is why doesn't the power cancel out? If you connect the output of an AC generator to a resistive load, then the net charge motion is zero because the current keeps changing direction; but the net power delivered to the resistor is positive because every time the current changes sign, the voltage also changes sign such that their product (power = current × voltage) always is positive. – Solomon Slow Jul 27 at 17:25
• To me, it seems like the current's value swings to say 2 amps, but then when the magnet turns around, you get -2 amps. So why isn't the net current 0 amps? – Jay Jul 27 at 18:50
• "Net current" isn't a phrase that I've heard before. What does it mean? There's instantaneous current, which continually changes sign in an AC circuit, and there's Average current which, when taken over any number of full cycles of the waveform, always is zero.There is also RMS Current, which electrical engineers use in power calculations. RMS always is positive by definition. But what is "net" current, and why are you asking? – Solomon Slow Jul 27 at 22:14
• All you have to do is accept that current can do useful work when flowing in either direction. If the load is a resistor, that happens automatically because the direction that does useful work is determined by the Voltage, and the current and the Voltage always switch direction together. If the load is a motor,... There's different kinds of motor. One kind uses current the same way a resistor uses it. Another kind of motor always rotates in sync with the AC frequency so that whichever way the current is flowing, the motor always is in position at that same instant to use it. – Solomon Slow Jul 29 at 12:12