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I know about how electricity is formed thanks to explanations of people on this website ,but what I really don't get is how a negative voltage works,when it occurs .Likewise for negative currents.

2007-07-28 03:06:19 · 11 answers · asked by Anonymous in Science & Mathematics Engineering

11 answers

Voltage is the potential difference between two points. Voltage is your electrical pressure. as compared to water pressure
current is your electrical flow: as compared to water flowing in a pipe. flow rate.

Current will always flow from the higher potential difference to the lower potential difference!

There are two different theories: Both work just as good as the other.

The first theory is the electron flow theory used by Electronics engineers.

The second theory is the conventional current flow theory or as it is also called the hole flow theory is used by electrical engineers.


In the electron flow theory the electrons flow from the negative terminal to the positive terminal.

In the convention current flow theory the current flow from the positive terminal to the negative terminal. But in the conventional theory it is not electrons flowing it is the holes left by the electrons as they drift toward the positive teminal hence the term hole flow theory.

The negative terminal is the terminal with an excess of electrons.
The positive terminal is the terminal with an excess of holes where electrons used to be until they were forced to drift through the power source to the negative terminal.
That is what gives you your potential difference. between the negative terminal and positive terminal.

Actually you shouldn't say negative current flow because current is either flowing or it isn't. It doesn't make any difference which direction down the wire it is going.

In a DC circuit current is always flowing the same direction from negative to positive if you are using the electron flow theory.
If you are working with the hole flow or conventional flow theory the current is flowing from the positive terminal to the negative terminal.

In an AC circuit current flows in one direction for the first half of a cycle Hz for the next half cycle Hz it flows in the opposited direction.
But get confused thinking it is negative current flow. It isn't.

What is going on is the polarity of the terminals changes.

I am going to use electron flow theory for this example:
During the first half of the cycle terminal A is negative and terminal B is positive. And current (electrons) is flowing form terminal A to terminal B.
The the second half of the cycle terminal A becomes positive and terminal B becomes negative. So the current (electron) flow is from terminal B to terminal A.
Then it repeats itself over the next cycle (Hz) hence the term alternating current..

Now I am going to really confuse you. Because inside the power source current flow is different it is backwards.

Like I stated before current flow is from negative to positive (electron flow theory) That is outside the generator or battery. inside the generator or battery current flow is from positive to negative. Confusing eh!

Don't be you are just completing the circle:(circuit) here is the whole picture.

When you complete the circuit current electrons) flows from the negative terminal through the conductor to the load (motor light heater etc) through the load back to the positive terminal of the generator or battery. It then (electrons) flow from the positive terminal through the generator or battery back to the negative terminal.

Hope that clears it up for you a little.

2007-07-28 12:46:55 · answer #1 · answered by JUAN FRAN$$$ 7 · 2 0

Negative Dc Voltage

2016-10-18 02:30:56 · answer #2 · answered by ? 4 · 0 0

Blame Benjamin Franklin. He chose negative for the electrons. It would have been easier if he had chosen positive for those dudes because they are the ones who do the moving. However, we can still have positive current if we imagine that the space the electron left empty as it began to move is positive. The space is indeed more positive than the electron and soon it will be filled by a different electron. But that electron is leaving a space empty, so the space is "moving" in the opposite direction of the electron flow giving us positive current. The spaces are normally called "holes" and now you understand "Hole Theory." So Positive and Negative current are just two ways of describing the same current. Positive and Negative voltage are two ways of describing the same voltage. A battery terminal is either more positive or more negative than the other terminal on the battery. It is relative.

2007-07-28 03:57:44 · answer #3 · answered by gunboss 1 · 1 1

The distinction is merely based upon what refernce point to choose to measure voltage from. You get an negative voltage on a car battery just by reversing the leads of your tester. In that case the positive terminal reads negative with respect to the negative terminal.

But to use the ever popular water flow in a garden hose analody, its a pretty high pressure when you put your thumb over the hose outlet because its all downhill quite a ways from the top of the water tower. But if you pull that same hose all the way up to the catwalk on the water tower, you slowly notice the pressure deccrease as you climb up, then as you get high enough you actually feel a suction on the hose end. That all happens because at different times you are at different elevations with respect to the surface of the water inside the tower tank.

I hope thats not too long winded.

2007-07-28 03:30:36 · answer #4 · answered by Like, Uh, Ya Know? 3 · 2 0

A negative voltage current just depends on the flow. If battery runs from positive to negative, that is a positive voltage. Reversing it gives a negative voltage. Same applies to current. Negative just implies that voltage/current are flowing opposite way. Very similar to negative distance in physics.

2007-07-28 08:54:19 · answer #5 · answered by james w 5 · 0 0

That usually refers to a system in which one of the two supply wires is grounded. In a car for instance the negative one is usually connected to the car chassis and all of the voltages (or currents) you would measure are all positive with respect to that chassis.

Suppose instead you connected the positive wire to the chassis (as some older cards did). Then you would measure negative voltages with a lead on the chassis (the positive one of the meter) and the negative one being used to look at voltages.

Similarly to those voltage readings, a meter could measure the current flowing to a positive or negative ground conenction and see a negatiive current or a positive current.

2007-07-28 05:01:22 · answer #6 · answered by Rich Z 7 · 0 0

The crucial point is negative and positive are just a matter of definition. It is quite typical in physics and engineering to arbitrarily choose a positive direction. The opposite direction is then negative.

A voltage is a difference in potential between two points. Either point can be used as a 0 volt reference. If point A has a higher potential than point B and point B is the reference Point A will be called positive. With the exact same setup point A could be used as the reference (and defined as 0 volts) in which case point B would be said to be negative.

2007-07-28 10:03:14 · answer #7 · answered by Anonymous · 0 0

First off, voltage is the cause, current is the effect. Like I answered in your previous question, voltage pushes/pulls current. And generally, if you have a voltage source, like a battery, it has one positive terminal AND one negative terminal. A battery can't just suck electrons into it's positive terminal forever, the thing would fill up with 'trons, so for every electron it sucks in at the positive terminal, it has to push one out of the negative terminal. A voltage is a difference of potential, and for there to be a difference, there has to be 2 terminals. If it only had 1 terminal, how could you have a difference? And where would all the sucked-in electrons go?

Okay, so you have your 2-terminal battery that has a potential of 1.5 volts across its terminal. Then both of the following are automatically correct:

1) The positive terminal has a voltage of +1.5 volts with respect to the negative terminal, and will pull one electron in for every electron that is pushed out of the negative terminal.

2) The negative terminal has a voltage of -1.5 volts with respect to the positve terminal, and will push one electron out for every electron that is pulled in the positive terminal.

It all depends on you point of view.

2007-07-28 03:53:07 · answer #8 · answered by Gary H 6 · 5 0

It means that the flow of electrons is going the opposite way than you are currently measuring. Usually if you have a negative voltage or current, you have the inputs wired backwards. You may also have the leads on your DVM backwards also.

2007-07-28 11:06:10 · answer #9 · answered by Anonymous · 0 0

A negative voltage is caused by an excess of electrons. A positive voltage is a deficiency of electrons.

2007-07-28 03:11:26 · answer #10 · answered by Randy G 7 · 0 0

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