Liquid-in-glass thermometers are based on the principle of thermal expansion of substances. A liquid in a glass tube (called a capillary) expands when heated and contracts when cooled. A calibrated scale can then be used to read off the respective temperature that led to the corresponding thermal expansion. Such thermometers are also called capillary thermometers.
In liquid-in-glass thermometers, the thermal expansion of liquids is used for measuring the temperature!
Thermometric liquids
The liquids used in such thermometers must have certain properties in order to be suitable for use. For example, they must not freeze at low temperatures, which is why water, for example, is not suitable. The liquids should also have a sufficiently high boiling point so that they do not vaporize at high temperatures. Furthermore, the liquid must expand evenly with the temperature in the measuring range used. Otherwise an uneven division of the scale on the thermometer would be necessary. Also for this reason water is not suitable, since water expands unevenly due to the density anomaly.
However, liquids which have all the required properties and are therefore suitable for use in liquid-in-glass thermometers are also referred to as thermometric liquids. In the past, the highly toxic mercury was used, which has a solidification temperature of -39 °C and a boiling temperature of 357 °C. Nowadays, usually blue or red colored ethanol (alcohol) with a melting point of -115 °C and a boiling point of 78 °C is used instead of mercury. In this temperature range, the everyday temperatures in the range between -20 °C and +50 °C can be well covered.
Measuring sensitivity
The measuring sensitivity of liquid-in-glass thermometers increases with the amount of liquid in the thermometer. The more liquid there is, the more liquid will expand and rise in the glass tube. For this reason, liquid thermometers have a reservoir to increase the amount of liquid in the thermometer. Too much liquid, however, would cause the thermometer to react very slow to temperature changes, as the heating of the liquid will take longer and the liquid will take longer to adapt to the outside temperatures to be displayed.
Note
Mercury was/is used not only because of the wide temperature range (theoretically applicable from -39 °C to 357 °C) but also because mercury hardly wets the glass tube. The capillarity is therefore lower and the temperature can be displayed and read off more accurately.
Liquid-in-glass thermometers are based on the principle of thermal expansion of substances. A liquid in a glass tube (called a capillary) expands when heated and contracts when cooled. A calibrated scale can then be used to read off the respective temperature that led to the corresponding thermal expansion.
The principle is relatively simple and hinges on thermal expansion. As the temperature around the thermometer increases, the liquid inside the glass tube expands and rises.Conversely, when the temperature drops, the liquid contracts and falls.
Liquid-in-glass thermometers measure the thermal expansion of a liquid, which is placed in a solid container, on a length scale. The mercury thermometer is one example of liquid thermometers. Alcohol is also used with this type of instrument. The temperature range is −80 to +330 °C depending on the liquid.
A liquid in glass thermometer can be used to measure temperature. They are the standard thermometers with which you are probably familiar, and are quite fragile, being made out of glass. As the temperature rises, the liquid inside the thermometer (either mercury or alcohol) will expand up the narrow tube.
The principle is that the color of the reflected light of the thermochromic liquid crystal changes with temperature. It then uses an image acquisition and processing system to correspond the temperature to the color to obtain the temperature distribution of the measured surface.
A thermometer works on the principle that solids and liquids tend to expand with temperature. When a thermometer lamp is immersed in a given solution or substance, mercury begins to rise. This increase in mercury is studied on a temperature scale.
The red line on the thermometer changes when it is heated or cooled. When a thermometer is heated, the red liquid inside the narrow tube expands, causing the liquid to rise, or go up, in the tube. When the thermometer is cooled, the red liquid inside the tube contracts, causing the liquid to go down inside the tube.
Water cannot be used in thermometer because of its higher freezing point and lower boiling point than other liquids . If water is used in a thermometer , it will start phase change at 0oC and 100oC and will not measure temperature , out of this range .
Glass lab thermometers are undeniably capable of delivering precision. In fact, certain industrial models filled with mercury can achieve an inaccuracy as low as ±0.15%. This high precision makes them a valuable tool in fields where even slight deviations in temperature can impact outcomes.
A thermometer is usually made up of a small, hollow glass tube. At the bottom of the tube is a bulb, which holds a liquid such as alcohol or mercury. When there is an increase in heat, the liquid inside the bulb expands, pushing up into the tube.A decrease in heat lets the liquid contract, moving down the tube.
A liquid in glass thermometer becomes sensitive when: For a slight change in temperature, the height of the liquid column changes more. The capillary tube shouldn't be too small and the bulb should be of a moderate size. Heat capacity rises with bulb size, and if the bore is too small, the liquid cannot flow freely.
In summary, increasing the size of the bulb, using thinner glass walls outside the capillary tube, decreasing the size of the bulb, and using a narrower capillary tube are all potential methods for increasing the sensitivity of a liquid-in-glass thermometer.
The red liquid used in some thermometers is typically a type of alcohol, such as ethanol or isopropanol. This liquid is dyed red to make it easier to read the temperature.
Introduction: My name is Neely Ledner, I am a bright, determined, beautiful, adventurous, adventurous, spotless, calm person who loves writing and wants to share my knowledge and understanding with you.
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