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If electrons travel from "-" to "+" and voltage decrease going through resistor why is voltage higher at positive wire instead of negative wire?

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An unfortunate convention.

Conventional Current assumes that current flows out of the positive terminal of a source.

Electron Flow is what actually happens and electrons flow out of the negative terminal of a source

When Benjamin Franklin was writing up his discovery, at the time without any detailed knowledge as to how it was actually occurring, he had a choice what is to be labeled positive and what is to be labeled negative.

enter image description here

image credit http://xkcd.com/567/

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  • \$\begingroup\$ Hence, when we look at current we are looking at the flow of "holes". en.wikipedia.org/wiki/Electron_hole It becomes more useful to talk about this when you get into the field of microelectronics. Here is a nifty animated gif that explains it: radartutorial.eu/21.semiconductors/pic/p-leitung.gif \$\endgroup\$
    – Nick
    Aug 5 '14 at 23:54
  • \$\begingroup\$ By the way, current is NOT a flow of electrons. it's a flow of charges [A] = [C/s] \$\endgroup\$
    – Blup1980
    Aug 6 '14 at 5:18
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Electrons have negative charge, and hence where they come from has negative relative voltage (since energy here is positive).

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Voltage is the difference in potential between two points, so to say a given point has a given voltage is meaningless unless you also specify the point you're measuring against.

If you're measuring against ground, with the negative terminal of the power supply (let's call it a battery) grounded as in your sketch, then by definition the negative side of the battery has zero voltage because you are measuring the potential between ground and ground. There isn't any. But the positive terminal has a voltage of one volt.

If you were to remove the ground from the negative terminal and ground the positive terminal instead, the positive terminal would have zero volts (again, with respect to ground) and the negative terminal would have (negative) one volt--the higher voltage.

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