eli5: how does AC power provide power when it’s just shifting back and forth? Don’t you need to have current going in one direction
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Depends on the device, if it’s a heater, ac electric motor or a non-led light then no, straight AC is fine. But many, if not most, devices have a AC to DC converter in their power supply.
AC is just much more efficient at transporting power over large distances.
Why would you need a current going in one direction all the time? You will have a current going in one direction for a period of time then it go in the other direction.
Compare it to if you have a battery and an incandescent light. It works I the battery is in the same direction all the time but is alos works if you flip the battery around once per minute. This is AC with a frequency of 1/60 Hz.
Instead of physically flip the battery add a switch so you can change how they are connected by moving the switch. You can now flip the switch every second and the lamp is still on and you have 1Hz ac. Now flip the switch 50 or 60 times per second and you have the main AC frequency around the world.
Now the question is why would flipping the switch often stop the lamp from emitting light?
If you look at it more carefully you will see the capacitive and inductive effect that results in a voltage that not immediately rises to full voltage so it will not be identical to if you do not switch but you still will have energy transfer.
There are losses in AC that do not occur in DC and for the same voltage and wire DC is in fact the more energy-efficient way you transmit power. The reason AC is used in the power grid is voltage change is a lot simpler with it and the main way to reduce energy losses in the power line is to have a high voltage.
It’s like asking “how does a bike move forward when you just move your legs up and down. Don’t you need to push it forward to go forward?”
The energy of the shifting movement can be transformed into the form of energy that you need to run your electronics.
Like the other comment mentioned, some simple electronics can run directly off AC because they just use resistance to produce energy from the “shifting” electricity in the wires, regardless which direction it’s moving any any given moment. More complex electronics will use circuits which can change the alternating flow to a one directional flow. One way this can be done is using an electronic circuit called a full bridge rectifier. This circuit has two paths for electricity to flow, but they each allow electricity to move in one direction (imagine a pipe of water with a one way valve). Since there are two of them, set to move in each of the two alternating directions, the electricity can be channeled into one direction.
When the electricity shifts left, it goes into the left pipe, which sends it forward. When the electricity shifts right, it goes into the right pipe, which also sends it forward.
Of course it’s far more complicated than that, but in essence, that’s how it works.
Think of a long river. If it flows continuously, you can extract power from the river’s current by dipping in a paddle-wheel. You can transfer power from the rotating paddle wheel by means of shafts, and finally use the power to turn a stone and grind grain into flour..
But if the water is just shifting to and fro – flowing forward and then flowing in reverse – you can still dip in the paddle wheel. Even if the paddle wheel turns one way once and then the other way, that motion is still power which you can use to turn a stone and grind grain into flour.
Any kind of motion or current does contain power. It’s up to you how to extract it.
A saw only goes back and forth, but it does a ton of work on the wood and generates heat.
It’s the same principle, just with electrons. The electrons aren’t all flowing in one direction, but they do still work when they are moving back and forth, therefore they impart heat, energy, etc. to the process.
It’s not like “moving the other way” somehow cancels out your initial move, any more than pulling a saw backwards undoes the cutting it did going forwards.
Some good answers here but I wanted to add, the power doesn’t come from the electrons, it comes from the electric field. The fields is generated regardless of the direction of the current. The field may invert, but it’s still present, and some devices don’t care which way the field is aligned.
To do “work”, in the physics sense, the voltage and current have to be going the same way. In AC, instantaneously in time, they are (if you have a high power factor load). Integration over an AC cycle, the AC is doing real work. When the voltage is negative, the current is also negative, so the (instantaneous) power is positive.
You can think of AC current as pulsating, moving back and forth like a wave. The wave sweeps out, and then back. Now when there is no load, the electricity is not moving. Think of a boat that reduces the wave and less water comes back to shore.
A load on the circuit causes the electricity to move and burns up the electricity. So you can think of the electricity as pulsating or going back and forth against a filament in a lightbulb. The filament “uses up” that electricity in both directions so there is a reduction in the electricity.
Let’s use a water analogy: You put a turbine in some flowing water and the turbine spins due to the water pushing on it. The direction the turbine spins is based on the direction of the water flow and the tilt of the blades of your turbine. When the direction of the water switches, if you also switch the tilt of the turbine blades the turbine will continue to spin in the same direction. You could also put your turbine in a side channel with a series of gates that switch so the water always flows in the same direction through your side channel. Or you could hook your turbine up to a gearbox and and output shaft and just shift it into reverse gear when the water switches and the turbine direction switches so that the shaft will always rotate in the same direction.
The point is that there are a variety of engineering approaches that allow you to take back and forth motion and convert it into continuous motion. Motion is energy, and thus one can design a setup that converts this back and forth movement into one directional energy flow.
The engineering approaches used for electricity are different, but accomplish the same task so your motor will always rotate in the same direction, even though the current is switching directions and now you have a spinning electric motor that can be used to power other devices.
Electricity can be a very complex topic. There are direct current (in line) and AC alternating current motors and electrical components.
First realize the electrons are already there in the wires. What your doing is pumping/moving/jumping electrons when you give them an energy source.
Its like a straw filled with water(not the best example but how i like to think of it)?
The wires are full of electrons ready to be moved/flowed in either direction, and they are always there as long as the metal is there.
(Chemical property of metals is that the outer valence shells are loose and you can pump electrons from one another atoms).
Photoelectric effect illustrates this. OR better yet, when you put metal in a micro wave. Your using microwaves to slam an electron off its valance shell. Power source(microwave) to knock an electron off.
Now to generate ‘power’ in a motor all you do is need one electron to pass through motor. It can pass going one way or the other. As long as an electron passes through the AC motor it receives current which it then uses to create power.
So as long as there is a circuit. (everything connected) Everything will flow.
AC power source – (wire) – AC motor – (Wire) – (Back to AC source) It will work. If the circuit isn’t complete the current(electrons) cant flow anywhere.
Looking at this from the view of the motor. Electrons can come in from the left and push out from the right and we get energy. If electrons come in from the right and push out from the left we get energy.
So its kinda like the same two electrons moving in and out of the motor create the electricity required to make it flow.
(In reality its probably like way more electrons but im trying to explain like this for simplicity. You can even calculate the electrons using 1.6 x 10-19 Coulombs of charge lol)
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