I think it'd be pretty difficult to do for arbitrary liquids, because i imagine there would be some non-trivial temperature gradients. You'd probably have to ac

I think it'd be pretty difficult to do for arbitrary liquids, because i imagine there would be some non-trivial temperature gradients. You'd probably have to account for the heat capacity and thermal conductivity of your soup to get it close to right. Simpler and cheaper to just use an old-fashioned thermocouple that clips onto the mug wall or something.