# Why Does a Wire Melt? | Current & Resistance Explained

• i.am.lost
In summary, the wire melts due to the heat generated by passing too much current through it, which is calculated using P = I^2/R and the heat capacity of the wire. Resistivity is a measure of resistance per unit length, while resistance is dependent on the length of the wire. However, resistivity is not simply resistance divided by length, as shown in the example of a 2m wire with a resistivity of 5 Ωm. This is due to the conversion of potential energy into heat energy, causing the wire to melt if the temperature reaches its melting point.
i.am.lost
Hi all,

I have been set an experiment of relating to the current needed to melt a wire (predominantly dealing with R = ρL/A). This sounds like a really dumb question (because it is ) but why does the wire melt when too much current is passed through?

Also, what is the correlation between the current that would melt a wire and the wire's resistance? And what the heck is the difference between resistance and resistivity (let me guess, resistivity is a standard measure, whereas resistance is length-dependent??)

Any help would be great. Many thanks you guys, and hope your day is going good.

The wire melts due to generated heat (given by P = I^2/R and the heat capacity of the wire) which of course comes from resistance.

Resistivity is just a sort of "resistance density" if you will. In classical physics you have a lot of these "density" type quantities like pressure, density (who'd have thought), etc. It's resistance per unit length, and nothing more - ohms per metre, Ω/m, Ωm^-1, etc, etc. Resistance is length dependant as you say.

A little bit of dimensional analysis goes a long way here.

Note that the unit of resistivity is Ohm metre Ωm and not Ω/m.

dst said:
Resistivity is just a sort of "resistance density" if you will. In classical physics you have a lot of these "density" type quantities like pressure, density (who'd have thought), etc. It's resistance per unit length, and nothing more - ohms per metre, Ω/m, Ωm^-1, etc, etc. Resistance is length dependant as you say.
It's resistance per unit length, and nothing more - ohms per metre, Ω/m, Ωm^-1, etc, etc.

Not exactly.

If the resistivity of a wire 2m long and having area of cross-section $$1 cm^2$$ is 5 Ωm, then the resistance is not 5*2 Ω. Resistance will be $$\frac{5*2}{0.0001}$$Ω

Last edited:
Due to resistance there is a drop in potential. This potential energy is converted into heat energy and if the T reaches the melting point of the wire, it melts!

## What is current and how does it relate to wire melting?

Current is the flow of electric charge through a material. When a wire is subjected to a high current, the electrons in the wire collide with the atoms, causing them to vibrate and generate heat. This heat can eventually cause the wire to reach its melting point and melt.

## What is resistance and how does it affect wire melting?

Resistance is the measure of how much a material opposes the flow of electric current. A wire with higher resistance will generate more heat when a current passes through it, which increases the chances of it melting. Therefore, a wire with a higher resistance will melt faster than a wire with lower resistance when subjected to the same amount of current.

## Why does a wire melt at a specific temperature?

Each material has a specific melting point, which is the temperature at which it changes from a solid to a liquid state. When a wire reaches its melting point, the atoms in the wire have enough energy to break their bonds and become a liquid. This temperature is determined by the structure and composition of the wire material.

## Can the thickness of a wire affect its melting point?

Yes, the thickness of a wire can affect its melting point. Thicker wires have a larger cross-sectional area, which means there is more material for the current to flow through. This results in a lower resistance and less heat generated, making it less likely for the wire to melt compared to a thinner wire with the same current passing through it.

## Is there a way to prevent a wire from melting?

Yes, there are several ways to prevent a wire from melting. One way is to use a wire with a thicker diameter, as this will have a lower resistance and can handle higher currents without melting. Another way is to use materials with a higher melting point, such as copper or aluminum. Additionally, proper wiring techniques and avoiding overloading the wire can also help prevent it from melting.

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