Thermometers are devices used to measure temperature, whether it is of an object or the surrounding environment. Dating back thousands of years, thermometers have advanced as fast as technology has, with newer and more accurate measurements. They come in a variety of forms with a variety of applications and contain a variety of parts.
Basics
Almost all thermometers are composed of two different parts: a temperature sensor that undergoes a physical change in response to a change in temperature and a means of indicating the value of that physical change. There are many different types of thermometers, but these two elements are found almost universally. The composition of these elements varies, though, depending on the type of thermometer, which correlates to its application, with some being more common than others.
Mercury Thermometer
One of the most common types of thermometers is also one of the simplest. Mercury thermometers are composed of a glass tube filled with a bit of the element mercury. The tube, which can either be a vacuum or nitrogen-filled, is extremely narrow with a bulb at the bottom, which contains the majority of the mercury. Mercury, which is a metal with a very low melting point, expands when it is heated and contracts when it is cooled. As the temperature increases, the mercury in the thermometer rises up through the tube as it expands, which is calibrated to indicate a given temperature.
Liquid Crystal Thermometer
These thermometers are commonly used for medical purposes. Composed of a single plastic strip containing heat-sensitive liquid crystals, they can be used to indicate the temperature of a patient by placing the strip upon the forehead, with the liquid crystals altering color depending on the temperature. They're also commonly found in mood rings. Liquid crystals are unique in that they have the properties of a liquid while simultaneously have the optical properties of a crystal. They're convenient but not nearly as accurate as mercury-based thermometers.
Alcohol Thermometer
Alcohol thermometer use principles very similar to mercury thermometers in that they are both composed of a single glass tube and an interior liquid. The alcohol is forced through a small capillary in the glass tube. Like a , it will move up the tube as the temperature rises. These are typically very accurate, but they tend to fade over time. There are four different types of alcohol typically used: ethanol, toluene, isoamyl acetate and kerosene, which are usually dyed either red or blue.
Recording Thermometer
These thermometers are used by meteorologists to study the changes in temperature of a given area over a given time. It is simple to make and is composed of a bimetallic strip that coils and uncoils in correlation with the temperature. The end of the strip contains a special pen which undulates up and down over a piece of paper that's constantly rolling, allowing the coil to physically record the temperature and its changes over time.
Tags: glass tube, different types, mercury thermometer, over time, physical change