I Current through Thin Wires

Tags:
1. Jan 15, 2017

Joshua L

Hey all, I've been thinking of a couple scenarios that involve thin wires (ones that have their diameter in the order of 1 mm). Suppose a gold wire with length L and diameter D is suspended straight in room temperature air and connected to some voltage V. Thus, a current will pass through the wire.

What must one consider when trying to analyze the wire? For example, would the (relatively) thin wire heat up significantly? Or, would enough of that heat be dissipated into the surrounding air so that any temperature effects can be ignored? Could the wire curl up? deform? And are there any other effects I haven't considered?

I'm just trying to learn more about the nature of thin gold wires. Any input from the community will be greatly appreciated.

2. Jan 15, 2017

oz93666

well... you can vary the current to get many different effects ...it will get hotter as the current increases ... a 1 mm gold wire should be getting warm to touch at perhaps 10A ... melt at perhaps 100A ..as for 'curling up ' I don't see why it should do that ...

gold is the second best conductor , (silver the best) ... neither oxidise or change on heating ...copper will oxidise .

3. Jan 15, 2017

Staff: Mentor

You need to know the resistance of the wire. You can calculate that from a property called the resistivity; googling for "resistivity electrical" will find the necessary formulas and lists of the resistivity of various substances including gold. Generally, resistance increases as wire is made the longer and thinner.

Once you know the resistance, the standard formulas for current and power ($V=IR$, $P=I^2R$) will tell you how much current is flowing through the wire and how much heat it must dissipate. How the wire reacts to that heat depends on the how thin the wire is and how much voltage you're applying.... But if you place a wire 1mm in diameter between the terminals of an ordinary 12 volt lead-acid automobile battery, it will quickly become glowing hot, burn, melt, and spatter little bits of molten metal in every direction. In fact, that's how fuses work - we deliberately place a length of thin wire in series in the circuit, so that it will melt and open the circuit if there is a short to ground.

4. Jan 16, 2017

Joshua L

Thanks for replying, but what do you mean that gold doesn't change on heating? Do you mean its conduction? And does such a property remain unchanged for only low-temperature differences, or for even high temperatures?

5. Jan 16, 2017

Staff: Mentor

You'll have to be more specific if you want more specific answers. How much heat are you talking about? Even solid steel will melt to liquid and then boil into vapor if it is hot enough.

6. Jan 16, 2017

David Lewis

Gold doesn’t corrode or oxidize when heated, but its resistivity does go up.

7. Jan 17, 2017

sophiecentaur

Have you thought of looking at one of the many lists of materials and their properties that are all over the Internet? Your eyes can do a better job of getting the information you want than a Q and A session on PF.