Flame and Magnetism
Name: Ralph F. O.
Date: Saturday, May 25, 2002
Why does a candle flame go out when you place a piece
of coiled copper wire around it? i.e., a piece of copper wire is wrapped
around a pencil to form a loose series of coils (5-6). It is held by
the straight piece that was not coiled, and the coiled portion is placed
around a candle flame so the flame is in the center. The flame
appears to go out but relights when the coil is removed.
The copper coil cools the gas envelope of the flame to the point where it is
no longer hot enough to enable combustion. I suspect that if you hold the
coil in the flame zone for a while after the flame goes out it would not
re-ignite because the combustion environs would cool below the ignition
point of the gases.
Combustion requires three things: fuel (wax here), oxygen (air here),
ignition temperature (a match here probably). Remove one and the combustion
stops -- that's the principles firemen use to put out fires. In the case of
your candle the high thermal conductivity of copper probably is conducting
sufficient heat from the flame that the flame goes out, but the heat
capacity of the melted wax, wick, etc. probably "holds" enough heat that the
temperature exceeds the ignition temperature if the copper wire is removed.
If this mechanism is operating you can test it by holding the copper coil
around the flame area for some time, so that the molten wax and wick cool,
the flame will not re-ignite when you remove the copper coil.
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Update: June 2012