A low DC voltage is produced by the thermocouple when the two junctions are at different temperatures. This voltage is referred to as the thermoelectric voltage. This thermoelectric voltage is produced by the temperature gradient along the thermocouple wires.
Re: What's causes the electric shock type pain in a tooth Hi DM69. I'm not a dentist but I'm pretty sure its the erosion of your tooth exposing the pulp, I had the exact same feeling in my tooth before I had it extracted a month ago, so I feel your pain.
Small cavities are occasionally sensitive to sweets, hot and cold. The sensitivity usually disappears once a filling is placed. Large cavities or a hit to the tooth and/or jaws can cause nerve damage inside the tooth. This pain is more constant and severe and may be referred to more as a throbbing pain. The most common signs of nerve damage are pain when biting, chewing, drinking something hot or cold, and swelling of the face or gums.