DC & AC

For dc all 'we' need to know is the polarity + or -

For ac 'we' need to know which is the 'live' phase and which is the neutral return cable.

John

Sorry to say the "current" is not going in different directions only the 'Voltage'! the Voltage is going in alternating swings from more than a neurtal point to an equal point opposite of neutral per cycle in time. The current follows. There is still a + side and a - side to AC it just happens 50 or 60 cycles per sec. (Hz) The current flow still goes from sourse to load.

DC direct current electron flow is from - to +. The load remains in a steady state. The current flow is in direct proportion to voltage.

If your first statement is true or positive, then your second paragraph is negative or false.

"current electron flow is from - to +. "

If your captioned statement from your second paragraph is True or Positive, than the current must change directions when the voltage changes polarity in an AC system.

Only one can be true or Positive and the other is false or Negative.

Try looking at the signal from a CT on an Oscilloscope or scopemeter. The signal will be an AC signal proportional to the amplitude of the current flowing through the CT.

If you have access to a GE PQM meter, look at the current per phase. It will show a really neat sin wave showing the current wave form along with the voltage wave form.

What...you are having a laugh....

Don't be silly....
If the voltage alternates in direction so does the current.

The actual electrons only move at drift velocity...so effectively with AC they shuffle back and forth at 50hzt (60 hz) hey don't actually travel down the wire.

Do your homework!

Well, I could be wrong but don't the electrons travel down the wire while they shuffle back and forth at 50hz. Or I should say they travel down the wire when there is a closed circuit. In an open circuit they would just shuffle back and forth?

Alternating = Back and forth. Not real net gain in travel if X number of electrons move Y distance in one direction and then X number of electrons move Y distance in the opposite direction. A billion to one odds they are not the exact same electrons each time but the net travel is still zero. The average Voltage of a sinewave is 0V and so the average current is 0A (again no net travel of electrons). That does not mean that no work is done, If I wave a paper fan back and forth the net travel is zero but I certainly move some air. The RMS value of a sinewave is is related to the effective Voltage, Current and Power Dissipation in a "RESISTIVE" circuit not the average voltage or current. A resistive circuit dissipates power regardlees of the current direction. It gets more complex with reactive circuits but I hope I got the basic idea across.

Yes you are wrong.

On AC the average voltage is zero over a cycle as it is a symetrical wave form..

Which way did you think the electrons would drift???

Alternating Current..

The clue is in the name!

I don't know what you have been doing at the university, but where have you been during basic physics class at college?

Wangito

In DC, signal (voltage/current) flow is from the positive to the negative electrode to complete a circuit.

In AC, there is slight modification in signal flow. Here the signal alternates in phases (50Hz or 60Hz depending on your country of residence)

Ultimately, the signal flows in phases from the live to the neutral to complete a circuit.

Furthermore, the phase is also positive and negative in nature.Thus in completing a circuit, the signal alternates between the positive and the negative amplitude of the waveform, 50 or 60 times per second.

Therefore, it is proper and more convenient to use ph & n in AC.

Same applies for + & - in DC.

Cheers,

ethobil

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

Thank you but from which pole does the electon leave the cell?

As Del said above, the electrons leave the negative terminal of a cell and travel to the positive terminal...

vice versa to 'conventional' terminology... As the electrons are negatively charged.

Just remember how a valve (tube) works, the cathode is heated to allow a cloud of electrons to form over the cathode, a positve charge on the anode attracts the electrons so causing a current to flow. If the anode was negatively charged the electrons would be repelled and stay at the cathode - Voila!! A DIODE!!!!!

John.

OK guys, i was probably suffering from the "conventional notation syndrom"..

Crossfire, thank you ones more for the link.

ethobil

Hi, Vikranth, if we look at "DCV" on an oscilloscope we see a "step" change from 0v to whatever static value it is, either in negative or positive direction (depending on which pole is referenced). if we look at ACV on the same setup we will see an alternating (sinusoidial) wave form that has both negative and positive values (rising and falling through a 0v reference with time). That is ACV has frequency and DCV doesn't. Now to answer your question: As we all know potential difference makes the current flow, so in the DC circuit this difference is stictly positive and negative, and in the AC circuit (since we have both positive and negative rapidly changing with time through the 0v reference), we can't use the DC convention (+/-), so we use phase (the effective or rms voltage of the waveform) in reference to neutral (0v) or earth for the required potential difference.