Behind of the development, of every sensor that we use at electrical test and measurement, there is some scientific description as How-to.
About K-type thermocouple, we know for example the basic theory, that two dissimilar metal wires when connected in series, their point of connection it works as voltage generation point, when this is exposed to heat or cold.
The more scientific description, this is named as spin Seebeck effect.
They are several websites which mention details about it, and therefore feel free to research more by your self, if you care to dive more in to this scientific description.