The emf is known as the Seebeck emf (or thermo/thermal/thermoelectric emf). The ratio between the emf and temperature variation will be the Seebeck coefficient. A thermocouple actions the real difference in possible across a cold and hot end for two dissimilar products. This likely change is proportional towards the temperature https://3alem-eladwa.com/category/%d9%83%d9%87%d8%b1%d8%a8%d8%a7%d8%a6%d9%8a-%d9%85%d9%86%d8%a7%d8%b2%d9%84/