# In an induction cooktop, what happens to the coils resistance when there is no pot? Does it vary between pots? How does the appliance respond?

An induction cooktop (or an induction rice cooker) uses a copper coil with a high-frequency alternating current going though. The magnetic flux heats any iron-alloy pot placed above.

But what happens to the coil's impedance when there is no pot (or any piece of iron)? My guess is that it would become a short circuit. As I understand, the magnetic core of a transformer/inductor is what gives it impedance (makes it resist alternating current), and I figure this would be no different.

How do they overcome the obvious problem of the coil being a short circuit? My guess is that it's current-regulated rather than voltage-regulated. An increase in resistance causes a decrease in wattage if the voltage is constant, but it causes an increase in wattage if the current is constant. Therefore, the coil would have low power usage when there is no pot and the resistance (or in this case, impedance) is low.

How does the choice of pot affect the coils impedance, and ultimately the power draw and heat output? Do bigger pots, or more ferromagnetic pots cause more impedance (in the coil)? Additionally; I realize that the heating of the pot comes from it's own electrical resistance, but how does this resistance affect the copper coils impedance?

EDIT: An earlier version of this question mistakenly stated that increasing resistance with constant voltage causes increased wattage, but decreases wattage with constant current. This was a mistake I failed to detect during proofreading (not a misunderstanding of Ohm's law), so I corrected it to what I intended in the first place. Some uses of "resistance" have been changed to "impedance" to accurately communicate the intended question. The question would be silly if it referred to true resistance.