Melting point of copper is around 1000 C. If you put a thin copper wire say 50 micron or so over a gas stove flame, it will break immediately. Has its melting point been reached? or, some other phenomenon is at work?
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$\begingroup$ What kind of fuel is this stove burning? $\endgroup$– Drew_JMay 20, 2017 at 23:17
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$\begingroup$ household gas stove- butane propane $\endgroup$– lkjhgMay 20, 2017 at 23:20
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$\begingroup$ How can you tell it's melted rather than snapped due to expansion strain or other causes? $\endgroup$– Carl WitthoftMay 22, 2017 at 17:37
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2 Answers
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The melting point of copper = 1,085°C (1,984 °F). Methane flame temp = ~1950 °C (3542 °F). Therefore, your thin filament copper reaches it's melting point very quickly.
Put a penny in the same flame & watch how long it takes for the penny to melt. It may not even melt if the flame isn't applied properly because copper is a great heat dissipator.
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$\begingroup$ so why penny will not melt but wire does, both are same material? $\endgroup$– lkjhgMay 20, 2017 at 23:34
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1$\begingroup$ thickness of material and heat transfer to support are some things to consider $\endgroup$ May 21, 2017 at 7:21
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$\begingroup$ if you want to try this beware modern pennies are mostly zinc. For copper you need one from the 70s or older. $\endgroup$– agentpMay 21, 2017 at 12:33
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1$\begingroup$ Actually, both are not the 'same material'. Your wire is very likely 99.9+% Cu. Pennies minted since 1982 are ~97.5% Zn & only 2.5% Cu. Pure Zn melts @ 419.5 °C (787.2 °F). Prior to 1982 pennies were ~95% Cu with varying amounts of (or lack there of) of Zn & Sn (tin). A 95% Cu penny may not melt because it is a larger mass than your Cu wire & because it takes longer to heat & while it heats, it dissipates a lot of the heat. It really depends on how much heat your gas stove puts out & how well you heat the penny. $\endgroup$– DIYserMay 21, 2017 at 19:41
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$\begingroup$ Your "Therefore" sentence is incorrect. What is true is that the Cu is exposed to a source temperature greater than its melting point. However, the wire (or other Cu object) will only reach that temperature if it cannot disperse heat (energy) fast enough. $\endgroup$ May 22, 2017 at 17:39
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Yes, the butane flame is melting the copper wire. According to Wikipedia butane torches can easily reach temperatures of $1430\unicode{xb0}C$. As you noted in your question this is well above the melting point of copper. In fact that maximum temperature that a butane flame can reach is nearly double the melting point of copper though this is hard to reproduce in real world applications.
The reason it can seem odd that the wire would break so easily is that metals are good conductors of heat. If the wire were much thicker the heat from the flame would wick away down the wire and be dissipated into the atmosphere. However with a thin wire the surface area to mass ratio is very large so the wire can heat up to its melting point before the heat has a chance to travel down the wire.
