What is 'alternating current'?

Question

I don't get it- how can current from the mains go in alternating directions? And where does it go back and forth between?

Is it shooting out of the plug and back in again to the power station?

zeb-that makes sense, but I don't see how AC travels along the mains wires. AC is used in the mains wires, but surely it is not going back and forth along the wires from the power station to people's houses?

Answer 1

Every circuit must have a loop. The current doesn't come out of the wall and then go back in. Let's assume you're looking at an outlet and you see the two slots where a plug would go. Let's say that first the current comes out of the left slot, goes through the appliance and then into the right slot. Then a fraction of a second later, the current comes out of the right slot, goes through the appliance and then into the left slot. In the US this happens 60 times per second. So, the current changes direction several times per second and is therefore called "alternating current."

The entire loop consists of the power generator, transformers, high voltage tranmission lines, transformers, wiring into the house, the appliance, wiring into the house, transformers, high voltage transmission lines, transformers and back to the generator. So, yes the loop is from the power station, all the way to your house and back again to the power station. This loop of current reverses direction 60 times per second in the US and 50 times per second in other places in the world.

It is only because of the alternating current characteristic that allows transformers to work. The transformers can step-up or step-down the voltage. Heat loss on the transmission lines is due to the resistance in the wires. The power loss in the wires is I^2*R where I is the current and R is the resistance. If the voltage is higher, the current is lower for constant power. Higher voltage means less current, so overall power transmission is more efficient. Typical transmission lines are at 110,000 volts whereas the voltage in a typical home in the US is 120V/240V. Being able to step up and down the voltage is the main advantage of having AC power instead of DC.

Answer 2

Basically yes.
But it still must have a complete circuit.
It is the movement of the electrons which transport the energy; not the electrons per se. It does not matter which direction they travel or how often they change direction, although the equipment must be compatible to work properly.
The electrons in your house wiring only travel to a local transformer. This transformer inductively couples the energy from the distribution grid to your local circuit.
The use of a circuit means that each appliance does not have to store a very large static electric charge for up to 1/120'th of a second before being able to return the charge to the grid.
High voltage static electric charges have all sorts of side effects that are difficult to manage.
Electrons are virtually massless so this constant reversing does not cost anything.

Answer 3

It alternates from + to - depending on the cycles per second, try wickipedia for a screen shot of the wave form it makes it easy to understand, alternating current is supplied by generators at the power station, and it goes back to the power station to complete the circuit after being measured by your house meter, direct current is supplied by storage batteries, it dose'nt alternate but is too dangerous for domestic use at the voltage we need.

Answer 4

Alternating current or AC is when the electrons move at 50 Hz or 50 times a second one way and then the other

Answer 5

AC power forms a sine wave alternating between positive and negative.
In the UK it alternates at 50 times a second (50 cycles) from negative 120V to positive 120V to give 240V.
In the US it's 60 cycles alternating between -55V to +55V to give 110V.
AC current can be transformed ..either 'stepped up' to higher voltage or stepped down lower.
The output of a power station is produced at thousands of volts for transmission of long distances and stepped down to usable voltages by transformers for delivery to industrial and household users.
(Direct Current (DC) cannot be transformed).

Answer 6

Because the neutral is connected to earth you are using 50 pulses of ac current a second . If it was only 10 pulses a second you would notice your lights going on and off.
You have to understand electron flow and hole flow to be able to understand how electricity flows in opposite directions.

Answer 7

It doesn't. It can fluctuate as needs are put on the resource. For example, in the UK voltage can differ between 230 & 250 volts. Battery sources (Direct Current) are usually stable, diminishing with expiry. A 9 volt battery would never suddenly increase to 12 volts.

Answer 8

ac current is when you get a feed from dc (direct current) it is transfered through a junction box and a unit called a transformer so that when you plug an electrical item into a socket the transformer alternates the current from the dc feed and gives the electrical item the correct amount of voltage that it needs and it also allows you to use another socket for another electrical item to work from the same dc feed in a different socket at the same time........if it wasnt for this system we would not be able to use electricity at home cos it would be to dangerous...

Answer 9

Direction is always changing.

Answer 10

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http://www.sunblock99.org.uk/sb99/people/DMackay/ac.html