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# Physics AC current watch

1. What does this mean? the current changes direction it says in my book. but that cant be correct. ive been told its to do with EM induction and the magnetic field. can someone please explain in GCSE laguage? Also can you explain DC?
2. Electricity flows in two ways, alternating current [AC] and direct current [DC]. Therefore, DC flows in one direction whilst AC flows in different directions, back and forth.

A magnetic field near a wire causes electrons to flow in a single direction along the wire, because they are repelled by the negative side of a magnet and attracted toward the positive side. Therefore, DC power from a battery was born.

AC travels farther without losing energy and could transfer different amounts of power. So, instead of applying the magnetism along the wire steadily, the scientist who worked this stuff out used a magnet that was rotating. When the magnet was oriented in one direction, the electrons flowed towards the positive, but when the magnet’s orientation was flipped, the electrons turned as well. So as a consequence, AC generators gradually replaced the DC battery system because AC is safer to transfer over the longer city distances and can provide more power.

Another difference is that the voltage of DC cannot travel very far until it begins to lose energy whereas AC's from a generate [in a power plant, say] can be moved up or down in strength by a mechanism called a transformer.

Sorry, I hope that wasn't too confusing or more than what you wanted; I tried to make it as short and sweet as I could.
3. no its fine i think. So the current swaps direction. The electrons move from the negative pole of the magnet to the positive pole of the cell is it? and vice versa?
and why doesnt it lose as much power?
4. Cells only provide DC!!!! AC is only provided by generators (like in power stations), or by microphones (but that's not usually a regualarly oscilating AC).

For the reason why AC loses less power, a good explanation of this is to do with Transformers.

As you know, only AC current can be used in transformers. Now, if you use a step down transformer (steps voltage down), you increase the current by the same factor (assuming 100% efficiency).

You should also know that P = I2 R (where P=power dissipated).

As a result, if you transmit high voltages at low currents, you reduce power (end so energy) losses. If you transmit the electricity as in the example above, you will increase the power/energy losses.

Since AC can be "transformed" (if that's the right word), it can travel further (but only in the right circumstances).

Hope that kind of helps! (Sorry - I'd be a dreadful teacher!)
5. ah its to do with national grid. ive been revising all night and searching the net. i eventually decided to ask someone who is an AS physics student. and that helped loads. thanks for all your help, wish me luck in the real thing!

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