in Physics by (157 points)
Why water cannot be used in thermometer instead of mercury? Why mercury is preferred than water in thermometer.

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by (2.3k points)

Why are we using Mercury in thermometer, reasons are followed:

  • The melting point of water is 0oc but when you see mercury freezing point (melting point) -38.83oc and the boiling point of the mercury is 356.73oc. The boiling point of water is 100oc. So based on this criteria the mercury is having the temperature reading capacity compared to water.
  • The color of mercury is silvery which is easy to identify and where as water is transparent and there is a chance of reflections of various colors.
  • The thermal expansion of mercury is 60.4 µm/(m·K) (at 25 °C). The thermal expansion of water is from oC to 100 oC - 4.2x10-2 the volumetric temperature expansion is non-linear respective to the temperature. But the mercury is linear temperature expansion can be observed. This is one of the main reasons to use of mercury in thermometers.
  • Water having the property of condensation but the mercury has no condensation property which is helpful to expect the exact values compared to water.
  • We can measure the negative and positive temperature by using the mercury but water cannot. Water is not helpful to measure below 0oC and above 100oC.
  • The most metals are solids at room temperature but the mercury is liquid form because it has high coefficient of expansion.
  • The mercury does not stick to capillary wall of thermometer and which can easily measure temperature accurately.