Types of Thermometer

• Every thermometer uses a physical property that varies with temperature, which is referred to as the thermometric property of the thermometer.
• The thermometric property of a liquid-in-glass thermometer is the thermal expansion of the liquid.
• The liquid-in-glass thermometer consists of a thin glass bulb joined to a capillary tube with narrow bore which is sealed at its other end.
• The liquid fills the bulb and the adjoining section of the capillary tube.
• When the bulb of a liquid-in-glass thermometer becomes warmer, the liquid in it expands more than the bulb, causing some of the liquid in the bulb to be forced into the capillary tube.
• The thread of liquid in the capillary tube increases in length when the bulb of a liquid-in-glass thermometer becomes warmer.
• The thinner the bulb wall of a liquid-in-glass thermometer is, the faster the response of the thermometer will be when the temperature changes.
• The liquid used in a liquid-in-glass thermometer usually contains mercury or coloured alcohol.
• Alcohol has a lower freezing point than mercury, making it more suitable for low-temperature measurements.