What is the purpose for frequency?

[johnbrown11]

So I have taken AC circuit analysis and electronics and stuff, but I was wondering what purpose frequency. Why its used with voltage and current.

[Averagesupernova]

That's a pretty broad question. Tell us what you know.

[DaveC426913]

So I have taken AC circuit analysis and electronics and stuff, but I was wondering what purpose frequency. Why its used with voltage and current.

Do you mean why do we commonly use alternating current instead of direct current?

[granpa]

capacitance and inductance are functions of frequency

[johnbrown11]

Do you mean why do we commonly use alternating current instead of direct current?

That and for example why we use 120V @ 60hz. Why the 60hz? Why not say..80hz? I am just a little confused on what the purpose it is for in AC or its function in electrical systems.

[Bob S]

So I have taken AC circuit analysis and electronics and stuff, but I was wondering what purpose frequency. Why its used with voltage and current.
Edison and Tesla had big arguments about the advantages of AC vs. DC. See

http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/physics%2010%20notes/Electrocution.html

Part of the advantage of AC was that transformers could be used (The transformer was invented in 1860 by Antonio Pacinotti). Edison thought DC was less dangerous (electrocution).

Bob S

[Zryn]

When you use transmission lines to take power from the coal fired power stations (which have to be built near large bodies of cooling water, and preferably near coal deposits) a transformer (two inductors) can step up the voltage (from the 11kV generators to say 22kV or 500kV or whatever) which steps down the current. The current causes the most problems in heat and loss of efficiency, so the bigger the voltage, the smaller the current, the less losses.

Transformers only work based on an alternating waveform (AC) and not at all on a direct waveform (DC).

Transformers are specially oriented inductors with a large lump of metal between them, which is much easier to design and build than the complicated semiconductor based electronics required to efficiently step up or step down DC waveforms.

Not all countries use 120V @ 60Hz. Australia uses 240V @ 50Hz for example. I would hazard a guess at the reasons being financial rather than scientific ('its how its always been done and its too hard to change now' + legacy equipment).

@ post #4: Capacitance and inductance are functions of geometry, capacitive and inductive reactance are functions of frequency.

[sophiecentaur]

Higher frequency than 50 / 60 Hz involves more transmission losses but, in Aircraft, I believe, they use (or used to) 400Hz because smaller components can be used (weight factor) but the distances involved are small.
DC transmission losses are lower but you have no easy way of voltage transformation. That may well change as technology advances, however - it's already done where there is no alternative.