A thermometer is a device used to measure temperature.
There are several types of thermometers, depending on how the temperature is measured.

  • Thermal Expansion: Uses the principle that the volume expands with increasing temperature. Mercury thermometer, alcohol thermometer, bimetal thermometer.
  • Thermocouple: Two metal wires of different types are joined together. Depending on the temperature difference, an electromotive force is generated in the metal wire, and current flows in the circuit. Measure the electromotive force and measure the temperature.
  • A material whose resistance varies with temperature: The resistance is measured to determine the temperature.
  • Measuring radiant energy: Every object emits different light (electromagnetic waves) depending on its temperature.