Imagine your morning going as follows: you wake up, proceed to the nearest countertop, and decide that your day should commence with the regular opening ceremony that consists of brewing your first cup of coffee. You bring out your electric kettle to heat up some water and proceed to fill it up and get it running.
This, then, may have some of you wondering how your particular “simple” kettle works when you swear it doesn’t have any onboard computer that precisely measures how hot the water is. Turns out, it still has a sensor inside it—it just relies on physics and materials science.
These particular types of thermostats are called bimetallic thermostats, and as their name suggests, they are composed of two dissimilar metals. These dissimilar metals, of course, expand when heated at different rates—an effect of their different thermal expansion coefficients.
From here, it’s just a matter of finding the right combination of metals. As the steam rises above the boiling water and enters the inner cavity of the kettle through a hole inside the vessel, it hits the bimetallic thermostat. This causes the thermostat, which is initially bent away from a nearby switch, to suddenly snap in the other direction—think of an umbrella suddenly turning inside out due to strong wind—and hits the nearby switch. This trips the switch, stopping the heating element.
This, then, leaves you with boiling-hot water and a kitchen that isn’t on fire; the bimetallic thermostat works precisely because it was designed to snap from one direction to the other when it heats up to the temperature at which water boils. Physics and materials science at work!
That’s what engineering is all about—it takes what we find out from science, and churns out methods and devices that use those concepts and phenomena to help us out as we go about our daily lives. Maybe give it some more thought over your next cup of coffee in the morning?
References
- Leigh, K. (2022, February 21). How stuff works: Your kettle. The Origin Blog. https://www.originenergy.com.au/blog/how-stuff-works-your-kettle/
- Woodford, C. (2011, January 7). How do electric kettles work? Explain That Stuff. http://www.explainthatstuff.com/how-electric-kettles-work.html
