Grades 3–5 · Machines
How does an electric iron keep its plate warm?
The smooth metal underside of an iron is called its soleplate. Inside the appliance, an electrical heating element gives energy to that plate. Metal conducts thermal energy, helping warmth spread from the element through the plate.
In the diagramAn iron warms a metal plate that presses fabricA thermostat controls electrical heating of the soleplateSensorHeaterOFFWarm soleplate passes energy into clothFabricAt the upper control point: heating switches off.
The plate meets fabric over a broad area. Energy moves from the warmer metal into the cooler cloth, while the plate also presses against it. As energy leaves the plate, its temperature tends to fall unless the element replaces that energy.
A thermostat provides feedback. It responds to the soleplate’s temperature and controls the electrical supply to the heater. In a simple switching system, heating stops at the upper control point and starts again after enough cooling.
The plate still contains thermal energy when the heater switches off. It can keep transferring energy during that interval. This explains why a heating indicator can turn on and off while the iron remains warm: the thermostat regulates the input as energy continues to move through the appliance.
About this explanation
Starting knowledge: Understand that a warm object can transfer energy and that a switch can stop electrical heating.
Sources
- United States Patent and Trademark Office · Google Patents — US5408769A: Thermostat control for an electric iron
- Tefal — Steam Essential Steam Iron: Thermostat and Indicator Light