An induction stove cooks food by using changing magnetic fields instead of a hot flame or a glowing heating element. A coil under the glass cooktop carries rapidly alternating electric current, which creates a changing magnetic field that reaches into the base of a metal pan. The pan itself becomes the heat source, so the cooktop surface stays much cooler than a traditional electric burner.
This makes induction cooking fast, efficient, and safer when the correct cookware is used.
The key engineering idea is electromagnetic induction, where a changing magnetic field produces electric currents in a nearby conductor. In an induction pan, these circulating currents are called eddy currents, and electrical resistance in the metal converts their energy into thermal energy. Many induction stoves also benefit from magnetic hysteresis losses in ferromagnetic cookware such as cast iron or magnetic stainless steel.
Power electronics inside the stove control the coil current, frequency, and delivered heating power.
Key Facts
- A changing current in the cooktop coil creates a changing magnetic field around the coil.
- Faraday's law describes induced voltage: emf = -N dΦ/dt.
- Eddy currents in the pan base produce heating by resistance: P = I^2R.
- Induction heating works best with ferromagnetic cookware such as cast iron or magnetic stainless steel.
- Thermal energy is produced mainly in the pan base, not in the glass cooktop.
- Efficiency is often around 80% to 90% because energy is coupled directly into the cookware.
Vocabulary
- Electromagnetic induction
- The process in which a changing magnetic field produces an electric voltage or current in a conductor.
- Eddy current
- A circulating electric current induced inside a conductor by a changing magnetic field.
- Ferromagnetic material
- A material such as iron that strongly interacts with magnetic fields and can be attracted to a magnet.
- Power electronics
- Electronic circuits that control and convert electrical power for devices such as induction stoves.
- Thermal efficiency
- The fraction of input energy that is converted into useful heating of the food or cookware.
Common Mistakes to Avoid
- Thinking the glass cooktop is the main heater. The pan is heated directly by induced currents, while the glass warms mostly by contact with the hot pan.
- Using nonmagnetic cookware. Aluminum, copper, and some stainless steel pans may not couple well to the magnetic field unless they have an induction-compatible base.
- Assuming induction works with direct current in the coil. A steady current would create a mostly steady magnetic field, but induction heating requires a changing magnetic field.
- Ignoring energy losses. Induction is efficient, but some energy is still lost in electronics, coil resistance, sound, and heating of nearby parts.
Practice Questions
- 1 An induction stove delivers 1500 W of useful heat to a pan for 4.0 minutes. How much thermal energy is transferred to the pan in joules?
- 2 A stove draws 1800 W from the wall and transfers 1530 W to the cookware. What is its efficiency as a percent?
- 3 Explain why a cast iron pan heats well on an induction stove, but a pure copper pan may not heat unless it has a magnetic base.