An induction cooktop heats a pan by transferring energy with a changing magnetic field instead of by heating a burner first. This makes cooking fast, efficient, and responsive because most of the energy is released inside the cookware. The glass-ceramic top stays relatively cool because it is not the main heat source.
It can still become hot from contact with the hot pan and spilled food.
Inside the cooktop, electronic controls send alternating current through a flat copper induction coil beneath the glass. The changing current creates a changing magnetic field that passes through the pan's base and induces circulating eddy currents in suitable cookware. Electrical resistance in the pan converts the energy of these currents into thermal energy, described by P = I²R.
Ferrous cookware works best because its magnetic properties strongly couple it to the changing field, concentrating energy in the pan.
Key Facts
- Alternating current in the induction coil produces a changing magnetic field.
- A changing magnetic field induces an emf: ε = -N dΦ/dt.
- The induced emf drives circulating eddy currents in the pan's base.
- Resistive heating in the pan follows P = I²R.
- The pan is the main heat source, while the glass heats mostly by conduction from the pan.
- Ferrous cookware, such as cast iron or magnetic stainless steel, couples strongly to the induction field.
Vocabulary
- Alternating current
- Electric current that repeatedly reverses direction, allowing the coil to create a changing magnetic field.
- Induction coil
- A flat coil of wire beneath the cooktop surface that creates the magnetic field used for heating.
- Magnetic flux
- A measure of how much magnetic field passes through a given area, such as the base of a pan.
- Eddy currents
- Circular electric currents induced within a conducting pan by a changing magnetic field.
- Ferrous
- Containing iron or having strong magnetic behavior that allows cookware to work effectively on an induction cooktop.
Common Mistakes to Avoid
- Thinking the magnetic field directly makes the pan hot. The changing field induces electric currents in the pan, and electrical resistance converts their energy into heat.
- Assuming any metal pan will work on induction. Aluminum and copper conduct electricity well but usually need a magnetic base because they do not couple strongly enough on their own.
- Believing the glass surface cannot become hot. The glass is heated secondarily by conduction from the hot pan, so it can remain hot after cooking.
- Confusing induction heating with a conventional electric radiant burner. A radiant burner first heats an element and then transfers heat to the pan, whereas induction primarily heats the pan itself.
Practice Questions
- 1 An induction cooktop delivers 1800 W to a pan for 4.0 minutes. How much energy is transferred to the pan in joules?
- 2 A region of a pan has an induced current of 12 A and an effective resistance of 0.50 Ω. Calculate the heating power using P = I²R.
- 3 A nonmagnetic aluminum pan and a cast-iron pan are placed on the same induction cooktop. Explain why the cast-iron pan heats much more effectively, even though aluminum is an excellent electrical conductor.