Why reverse polarity in alternating current?

Question

Electronics

What is the meaning of the polarity reversal? What is the practical advantage over direct current? No matter how much I searched, everywhere I see only an explanation of the alternating current and its graph, but why do we change the polarity n times per second?

Answer 1

At a minimum, this is convenient in terms of the fact that hundreds of kilovolts can be transmitted over power lines, and then brought to the usual 0.4 kV by transformers. The transformer is relatively simple and does not require electronics.
With a constant, such a focus will not work. Even at a few kV find semiconductors already hemorrhoids.
And transmitting low voltage will not work, because. superconductors have not yet been laid in every house, and without them, thousands of amperes cannot be passed to consumers. :)
And it's easier to do a change with a generator right away.
Electric motors at a break are simpler and do not require as much attention as brush motors at a constant. (Although now all this is somewhat changing, but it used to be very relevant)

Answer 2

It doesn't just change, it changes in a sine (or cosine) fashion.
This is very convenient for many reasons:
1) The derivative of the sine is the cosine. And it is the same in form, i.e. this is the same sine, only shifted by 90 degrees in phase. Those. devices that operate as a derivative (a transformer, or an inductor, for example) and the output is also alternating current.
2) The antiderivative of the sine is also a cosine (minus cosine). And here the same thing. If the device works as an integrator (capacitor, for example), then again, the shape remains unchanged.
All this greatly simplifies the formulas, as a result, you can simply draw vector diagrams instead of solving a bunch of integrals and derivatives
3) As mentioned above, AC electric machines are more reliable
4) The easiest way to get a sine is by rotating the circuit in a constant magnetic field.
ЭДС=-Ф(t)'=-(B*S*cos(w*t))'=B*S*w*sin(w*t)
The formula is "school", but the essence should be clear - we change the angle evenly ( alpha=wt ) and we get harmonic oscillations of the induction EMF at the output.