# Positive and Negative voltage.

Discussion in 'General Electronics Chat' started by Maintenance Man, May 12, 2010.

1. ### Maintenance Man Thread Starter New Member

May 12, 2010
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I am taking a Mechatronics class in which another student is telling me that there is no such thing as negative voltage. I was always told that there is positive voltage and negative voltages. Could someone please help me with this? Thank you in advance. This is my first post to this forum.

2. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
It all depends upon your point of reference.

In electronics, you need to declare a node in a circuit as your point of reference.

If you measure the voltage across the terminals of a battery, you will measure a positive voltage if you use the - terminal for your reference, and a negative voltage if you use the + terminal for your reference.

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3. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Voltage is an electrical potential in the same way that a mass has gravitational potential when it is raised to some height above the surface of the Earth. An object with gravitational potential can have that potential converted into motion by dropping the object.

Depending on the point of reference, either the ground or the top of a tower, our object will have either positive or negative gravitational potential.

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4. ### skkk New Member

Apr 5, 2010
3
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positive voltage or negative voltage means how do you chose polarityi.e( + to-) or (-to +)in a electrical circuit. after all its magnitude is same.use the concept of enery alway flow from higher potential to lower potential..take ur reference and calculate it

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5. ### Bychon Member

Mar 12, 2010
469
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The word, "convention" applies here. A convention is an agreement between "those in the know" about what to call something. The convention on this planet is that electrons have a negative charge. Electrons flow. Electrons repel each other. Electrons have mass and take up space (very little space).

As others have said, "negative voltage" is derived from your point of view at the moment. When you are examining a circuit, you simply declare where your reference point is and measure from there. Some voltages might be negative with respect to that point. You see, voltage is always measured as compared to someplace else.

It matters not whether your declaration is in agreement with the person next to you unless he is also working on the same circuit. It matters not whether you think in terms of electrons and holes, negatrons and plusatrons, or elephants and zebras...as long as it is a functional way to diagnose the circuit. Then, you convert to conventional terms when communicating with other people.

Last edited: May 12, 2010
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6. ### beenthere Retired Moderator

Apr 20, 2004
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We seem to endlessly split hairs on this one. But the series of experiments that established that electrons carry a negative charge was carried out in 1907 by Dr. Millikan - http://en.wikipedia.org/wiki/Electron . The charge is a factual quantity; the polarity is a convention.

Last edited: May 12, 2010
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7. ### Bychon Member

Mar 12, 2010
469
41
Sorry. I erroneously depended on something that I read in one of the electronics forums. I'll try to edit that out.

Last edited: May 12, 2010
8. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
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Indeed so, but charge is not voltage.

All voltage is relative and since I moved the reference point to minus infinity in 2010 all voltage is positive.

9. ### retched AAC Fanatic!

Dec 5, 2009
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A positive voltage is the voltage that pushes electrons out of a battery
A negative voltage is the voltage that pulls electrons into a battery

The voltage of a 12v battery is actually (+6v) + (-6v)

By pushing out 6psi of the (-) terminal and sucking 6psi into the (+), you end up with 12psi of usable force in the circuit.

If you have ever seen a battery become 'backwards' you will get this.

In a battery, you have the top half full of 'holes' and the bottom half full of 'electrons'

As the battery pushes electrons out the (-) and sucks electrons in the (+), the top starts to push the holes to the bottom. When there is an equal number of electrons on the top and bottom of the battery, it is at equilibrium. No sucking and pushing.

A battery charger "pushes" more electrons into the battery, moving the holes back to the top, to start again.

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10. ### Bychon Member

Mar 12, 2010
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I'm getting dizzy.

11. ### retched AAC Fanatic!

Dec 5, 2009
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Yeah, I dont even know if I believe it.
A negative voltage is different than a 'less than positive' voltage.

I think I need a aspirin.

12. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
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At the most basic level, an atom with an equal number of electrons and protons has no charge.

Remove or add electrons and you get an _absolute_ positive or negative charge.

Think of basic electrostatic experiments, friction to create charge - one item ends up positive and the other negative, due to tranfer of electrons.