Question

what is the principle used in the mercury thermometer​

Answer 1

Explanation:

These liquid thermometers are based on the principal of thermal expansion. When a substance gets hotter, it expands to a greater volume. Nearly all substances exhibit this behavior of thermal expansion

Answer 2

The principal used in any thermometer is expansion and contraction of liquid, i.e. mercury, according to the increase and decrease in temperature. When the temperature of body increases then mercury expands while when temperature of body decreases mercury contracts. The thermometer us labelled in any particular scale.