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Name: lois
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
I have been wondering why heating elements (in an electric stove, in a toaster, etc.) hum when turned on. I asked our physics teacher here at my school and he was unable to come up with a theory. Do you have any thoughts?



Replies:
I use a slight variation of this question for our application for employment test for our Engineers! Our question is more like "Why does a Soldering GUN heat up the tip. While the reason for the heat is different, the cause of the sound in a heating element and the source for heat in a U shaped soldering tip is the same. I would assume that the heating elements that the questioner is talking about is of the zig-zag type. The vibration that causes the sound (or buzz) comes from the pulsating eddy currents that "fight" the adjoining wire. Those eddy currents collapse at the rate of 60 hz in single phase applications. If the coil was DC, the reaction of this element would be different and probably silent. In a soldering gun, those eddy currents actually produce enough heat at the 180 turn that the tip heats enough to melt solder. Remember that the tip of a gun is actually a single turn of the secondary of a transformer in the gun. I am quite surprised at how few engineers get this answer on my test. In fact, most say that it is resistive!

sysop



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