Proposing a toast to the happy thermocouple.

Conductors. Voltage. Temperature gradients. And how design prevents accidents in a toaster.Two pieces of toast popping out of an old fashioned toaster


1-Minute NomNom

We all want to make that perfect piece of toast (read how in the 1-Minute NomNom “Don’t underestimate the power of the Dark Side”).  Newer toasters use a timer to determine how long the bread should be toasted. When the set time is up, a spring is released and out pops the bread.

In some older toasters, the same function was performed by thermocouples. Thermocouples are made of two different conductors (e.g. made of different materials), joined together at different junctions.

Diagram of a thermocoupleAt each of these junctions, the different conductors produce an electric potential according to that junction’s temperature.

When two or more junctions are at different temperatures, the difference is known as a temperature gradient. This temperature gradient produces a voltage. It is this voltage that was used to release the mechanism holding down the bread.

1979 patent, for example, details how the thermocouple responds to the different temperatures in the

Child hand catches toast bread slices flying out of a toaster1) toaster casing holding the bread

2) bread itself

3) air in the toaster

As the toaster casing, the air within, and the bread all heat up at different rates, they will be at different temperatures. A temperature gradient is created and a voltage is produced. At the right temperature gradient, the resultant voltage gives rise to a pulse. The pulse electronically releases the mechanism, and the bread pops up.

Second Helpings

Why is it necessary to build a toaster that pops out the bread? It is to keep us safe. The insides of a toaster are dangerously hot. Reaching in with our hands or any tool can easily become an accident. Bread that pops up makes it easier for us to take out our toast. It is an example of how an accident has been designed out of an appliance.

Feed Me!

What other examples can you think of where accidents have been designed out of household appliances? Share your thoughts with me!


Screen Shot 2015-01-10 at 6.02.39 pmLike this? You and I can be a happy thermocouple if you like me to discover more. All you need is a minute a day to explore the world’s marvels through the phenomenon of food!

photos: in order – depositphotos/Sandraliselightkeeper

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