AC / DC why not AV /DV?

I came close to register as anonymous for this one but I figured why not!
I've been asking myself this question for a while.

If a power source supply voltage and its load consumes current why don't we say AV and DV instead of AC and DC?

Since we don't necessarily know what the load is but we know what the supply source is.

Mike

you could but no one would know what you were talking about because you would be the only one using that terminoligy

Because they supply voltage, but devices consume current. We know what the voltage is, but at a given current draw the voltage can vary dramatically.
The load and the supply source are both REQUIRED to be known to characterize a condition, and the voltage allowance for a DC source is not a finite number and the AC variance is just as much unknown unless defined, in which case there are no questions.

I understand that I am not going to change the rule or anything for that matter and i also understand that both voltage and current are required. I was just wondering why it was called AC and DC since we are talking about voltage. The current comes after (when and if there is a load)

In other words if I see a wire and i or anyone is curious we would ask two questions or measure:
1 - How much voltage is there in this wire?
2 - Is it AC or DC?

At this point it doesn't have to have a load.
Maybe we call it AC and DC for the same reason we call a wall "A wall"?

Mike

A lot of electronic terminology is a lot older than electronics. This is a pretty good example of it.

In describing a supply, you can say it is 12Vdc or 12Vac. The DC or AC can be added for clarity. The V gives you the electromotive force; the DC or AC tells you if the current flow is steady state (direct current) or changes direction (alternating current).
Ehh. It is what it is.
kenjj

Quoting QuietMan: "A lot of electronic terminology is a lot older than electronics. This is a pretty good example of it."

Interesting point. Early discussions of possible electron flow thought there were particles at a higher potential (thus, positive) which would naturally flow to a lower potential (thus, negative). And an assumption was made as to which electrodes in a battery were positive and negative. Ohm had already published his theory of electron flow and the two factors (voltage and resistance) controlling the amount of current flow. Scientists had already observed the blocking characterisics of a selenium crystal (the early diode). Thus the arrow in the diode symbol was originally meant to indicate which way this positive flow would go when the switch was thrown. All electronic theories and equations were based on this positive-going flow.
So when someone thought to set up an experiment using high voltage to cause an arc across a gap, they thought they knew which way the sparks would fly, and would vindicate this + to - theory.
WRONG-O! The sparks really flew that day! (I couldn't resist... ) And now teachers are stuck telling students that electron flow goes AGAINST the diode's arrow, but holes (the positive ions) do go "the right way". And students have to think "reverse flow" when they use equations meant for "positive particles".

And now you know... the REST of the story!
(I am SO showing my age here!)
kenjj

lilimike said:

I came close to register as anonymous for this one but I figured why not!
I've been asking myself this question for a while.

If a power source supply voltage and its load consumes current why don't we say AV and DV instead of AC and DC?

Since we don't necessarily know what the load is but we know what the supply source is.

Mike

Click to expand...

Why do many people in Montreal speak French instead of English!

Could it be a matter of history not unlike your question?

To the ineffable all,

There is a lot of confusing and inexact descriptive terminology in the science and engineering fields. Some of it is perpetuated by people and organizations who should know better. Other times it is done because it was always done the wrong way, and no one has the courage to point out the right way. For instance, NASA used to call space suit excursions outside a space vehicle EVA (extra-vehicular activity). Since the first Star Wars movie was released, they started calling it "spacewalking". No journals or reporters ever asked NASA if the astronauts would walk away if their tether broke.

lilimike,

You are right to question the AC/DC terminology. It should be called alternating or sinusoidal excitation, and steady value or constant value excitation. I will leave it to you to select the abbreviations.

Another example is "power supply". It is actually a electrical energy supply. Its power, voltage, and current is a characteristic of the energy supply, yet folks insist on calling it by its characteristics instead of what it really is.

kjennejohn,

Current exists, but does not flow. Current is charge flow. To say "current flow" means "charge flow flow", which is redundant and ridiculous.

I hear a lot about Ben Franklin and others getting it wrong in naming the polarity of the electron negative. Actually it does not matter. There are just as many positive charge carriers in the universe as negative charge carriers like electrons. All electrical calculations should be done using the conventional polarity method. This assumes that a positive voltage source will output a positive charge carrier out the positive terminal. Then if is necessary to determine the actual direction of the real charge carrier, it is easy to say that a positive charge carrier in one direction is the same as a negative charge carrier in the opposite direction. This eliminates the wonderment of whether a charge carrier is positive or negative or which direction charge is moving. You already mentioned that semiconductor manufactures mark their products using the conventional polarity. Did you notice also that ammeters are marked the same way?

And finally I contend that Ohm's law is a property of a material which can be called electrical linearity, and is not V=IR. V=IR is the definition of resistance and should be called the resistance formula. There has been a fierce debate about this recently.

Ratch

Ratchit said:

You are right to question the AC/DC terminology. It should be called alternating or sinusoidal excitation, and steady value or constant value excitation.

Click to expand...

With DC we mean that the current is unidirectional i.e. current does not change direction. Current doesn't have to be steady at all to be DC. Half-wave rectified AC becomes DC, but the voltage or current isn't necessarily constant at all.

In AC the direction of the current alternates.. hence the name. AC could be constant in magnitude, but alternates in polarity (square wave inverters).

Sceadwian said:

Because they supply voltage, but devices consume current. .

Click to expand...

Current in = current out

ac/dc

you are right.It could be called AV/DV.but the other name was used popularily now.It will be a bit difficult to change the names now.
So why bother?

AC/DC just sounds better.

**broken link removed**

mister T,

With DC we mean that the current is unidirectional i.e. current does not change direction. Current doesn't have to be steady at all to be DC. Half-wave rectified AC becomes DC, but the voltage or current isn't necessarily constant at all.

Click to expand...

Yes, the "direct" in DC is not very descriptive, is it? Perhaps it should be called single polarity excitation, or single polarity pulsating excitation, or dual polarity excitation, etc.

Ratch

Ratchit said:

mister T,

Yes, the "direct" in DC is not very descriptive, is it? Perhaps it should be called single polarity excitation, or single polarity pulsating excitation, or dual polarity excitation, etc.

Ratch

Click to expand...

All are good examples of archaic electrical terms derived from classic words.

Latin directus "straight"
Latin alternatus "one after the other"
Latin currere "to run, move quickly"

for a deeper description theres also a term

Crest factor - Wikipedia, the free encyclopedia