Is voltage an inherent property of a metal at a given temp?

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Main Question or Discussion Point

I am trying to gain a very basic understanding of voltage. I understand amps and resistance, but not voltage. I am thinking of a copper wire that is used in a basic electrical circuit to light a light bulb. Is the voltage of this wire an inherent property of copper at a given temperature? If not, what factors affect its voltage?

Lets assume there is a battery made of copper wire. Would the electrolyte solution at the anode and cathode affect the voltage? What other factors would affect voltage?

Would doubling the diameter of the copper wife affect the voltage?

Thanks for any insight.
 

Answers and Replies

  • #2
ZapperZ
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I am trying to gain a very basic understanding of voltage. I understand amps and resistance, but not voltage. I am thinking of a copper wire that is used in a basic electrical circuit to light a light bulb. Is the voltage of this wire an inherent property of copper at a given temperature? If not, what factors affect its voltage?

Lets assume there is a battery made of copper wire. Would the electrolyte solution at the anode and cathode affect the voltage? What other factors would affect voltage?

Would doubling the diameter of the copper wife affect the voltage?

Thanks for any insight.
This all depends on your power source.

For example, if you attach a resistor to a battery, the battery will try to maintain a potential difference as much as it can, no matter how you change the resistance. So changing the resistance will not change the potential difference across the resistor.

If your power source is a constant current source, then yes, the potential difference will change because the power supply will try to maintain a constant current through that element, rather than maintaining a constant potential difference.

Potential difference here is very similar to gravitational potential difference. If anything, it should be easier to understand conceptually than current and resistance, not the other way around.

Zz.
 
  • #3
mjc123
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A metal, on its own, does not have a voltage. There is no such thing as "the voltage of copper". Copper wire in a circuit merely transmits the current. You need some sort of power supply to generate the current and light the bulb.
A copper electrode in contact with a solution of Cu2+ ions would have a potential, which is a measure of the propensity for an electrochemical reaction to occur (either the oxidation of Cu or the reduction of Cu2+).
If you connect this to another electrode with a different electrode potential, you will have a potential difference (voltage), and if you close the circuit current will flow.
For the Cu/Cu2+ electrode described, the potential will depend on the concentration of Cu2+, and on the temperature, but not on the dimensions of the copper or the volume of the solution. Electrode potential is an intensive property.
 
  • #4
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Thank you ZapperT and mjc23 for your help.

mjc23 has an explanation that I understand a bit easier.

Let me reply to some quotes and see if I can get even more insight.

A metal, on its own, does not have a voltage. There is no such thing as "the voltage of copper". Copper wire in a circuit merely transmits the current. You need some sort of power supply to generate the current and light the bulb.
Great point; however, if you have copper wire transmitting the current, as opposed to let's say, aluminum wire, but have the same power source, I assume you are saying this will not change the voltage, because the voltage is dependent only on the 2 electrodes, not the wire that transmitts the electricity. However, as a side note, this is should change the amperage if you change the wife, as alumunum electrons would flow differently than copper electrons in the wire?

If you connect this to another electrode with a different electrode potential, you will have a potential difference (voltage), and if you close the circuit current will flow.
Question: I would assume that an electrode with a low electronegativity flowing to an electrode with a high electronegativy would have much higher voltage than two electodes with similar electronegativity?
 
  • #5
Merlin3189
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I am thinking of a copper wire that is used in a basic electrical circuit to light a light bulb.
The wire does not light the bulb. The wire carries electric current. The current lights the bulb
Is the voltage of this wire an inherent property of copper at a given temperature? If not, what factors affect its voltage?
No.
You have a fundamental misconception about voltage (not surprising in view of how books write about it.) In the context of circuit electricity, voltage always refers to the difference between two points in the circuit. A single wire never has a voltage. A wire can only have a votage compared to another wire. So when you connect two wires to the ends of a 9 V battery, the difference between the wires is 9 V.
The wires simply serve to pass this difference along to the bulb and to carry any current which may (or may not) flow through the ulb.
The voltage difference across the terminals of the bulb, along with a characteristic of the bulb called its resistance, determines how much current can flow through it.

Lets assume there is a battery made of copper wire. Would the electrolyte solution at the anode and cathode affect the voltage? What other factors would affect voltage?
The battery cannot be made of just copper. You already know it also needs an electrolyte. As MJC has pointed out, you also need another different material, such as zinc. Both metals are in contact with the electrolyte and one, in this case zinc, dissolves more energetically than copper. As Zn atoms dissolve to make Zn++ ions, they leave electrons behind on the metal. The copper also tends to dissolve, but much more lazily!
If the two metals connected with wire in a circuit, the electrons at the zinc end flow through the wire to the copper end, where they actually attract any copper ions back and make them into atoms again. They will also attract hydrogen ions and convert them into atoms.

If the elctrodes are not connected, then a balance is reached between metal dissolving to make +ve ions , leaving -ve electrons behind, and the -ve electrons attracting the +ve ions back to convert them into atoms. As soon as you make a circuit and allow some elctrons to escape from the electrode, there is less -ve attraction and more atoms can dissolve to make ions.

The voltage difference between the copper and zinc ends, depends on the relative tendency of copper and zinc to dissolve as ions in the electrolyte. Zinc is pretty keen to dissolve, but copper is quite happy as it is.
Would doubling the diameter of the copper wife affect the voltage?
Not in the way you're thinking. Essentially, battery voltage difference depends on the materials of the two electrodes and on the electrolyte. Copper is copper and zinc is zinc, whatever size they are. But if the area of the electrodes are bigger, then there is more opportunity for metal to dissolve and the battery can supply a bigger current. The voltage will still be the same, depending only on the relative tendency for each atom to ionise.

There is a way the thickness of the wires can affect the voltage difference across the bulb. Copper wire is not a perfect conductor, so there is some voltage difference between the ends of a single wire when it is carrying current. Thicker wires need less voltage difference aong their length to make the current flow. So thicker wires mean more of the voltage difference from the battery reaches the bulb.
Thanks for any insight.
 
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Thank you, Merlin3189, that was very helpful!
 
  • #7
mjc123
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However, as a side note, this is should change the amperage if you change the wife
Changing the wife changes everything!

Seriously though, both copper and aluminium are used as very low (essentially zero) resistance current-transmitting wires. Most of the resistance in the circuit comes from the lamp, and that's what determines the current.
Copper and aluminium do have different resistivities (an intensive property), but the wire resistance (an extensive property) depends also on the dimensions of the wires.
 
  • #8
CWatters
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Materials have a property called resistivity that is a measure of its ability to conduct electricity. The actual resistance depends on the physical dimensions of the material as well as the resistvity. So a long thin wire has a higher resistance than a short fat one. The resistivity and resistance can depend on temperature but in many/most cases this can be ignored. Obviously there are cases such as incandescent light bulb filaments where it can't be ignored. If you are just starting to learn about circuits I recommend avoiding using light bulbs as loads.
 

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