Given below is the list of different types of thermometer. By the end of this section, you will be able to: Any physical property that depends consistently and reproducibly on temperature can be used as the basis of a thermometer. It merely provides you with an indication of whether the person has a fever or not. Before we look at how to read a thermometer, lets first see how thermometer finds out the body temperature. In most of the cases, we see thermometer using Mercury as a liquid to measure the temperature. The triple point is the unique combination of temperature and pressure at which ice, liquid water, and water vapor can coexist stably. Thus, a temperature difference of one degree on the Celsius scale is 1.8 times as large as a difference of one degree on the Fahrenheit scale, or ΔTF=95ΔTC.ΔTF=95ΔTC. 2. Figure 1.3 Because many physical properties depend on temperature, the variety of thermometers is remarkable. (a) In this common type of thermometer, the alcohol, containing a red dye, expands more rapidly than the glass encasing it. The triple-point temperature is defined as 273.16 K. This definition has the advantage that although the freezing temperature and boiling temperature of water depend on pressure, there is only one triple-point temperature. The results depend somewhat on the choice of gas, but the less dense the gas in the bulb, the better the results for different gases agree. As a result, it is not as accurate as of the first one on our list. Other properties used to measure temperature include electrical resistance, color, and the emission of infrared radiation (Figure \(\PageIndex{1}\)). Types of Thermometer. Therefore, a standard thermometer is required. On the Celsius scale, the freezing point of water is 0°C0°C and the boiling point is 100°C.100°C. Similarly, we find that \(T_K = T_C + 273.15 = 298 \, K\). Pro Lite, Vedantu The Kelvin scale is the absolute temperature scale that is commonly used in science. To convert between Fahrenheit and Kelvin, convert to Celsius as an intermediate step. © Sep 2, 2020 OpenStax. Experiments confirm the existence of such a temperature, called absolute zero. Such scales are convenient in science because several physical quantities, such as the volume of an ideal gas, are directly related to absolute temperature. Constant-volume gas thermometers are big and come to equilibrium slowly, so they are used mostly as standards to calibrate other thermometers. Other properties used to measure temperature include electrical resistance, color, and the emission of infrared radiation (Figure 1.3). On which mechanism does it work and what makes it provide us with accurate body temperature. This work is licensed by OpenStax University Physics under a Creative Commons Attribution License (by 4.0). (a) What is room temperature in \(^oF\)? If the results are extrapolated to zero density, the results agree quite well, with zero pressure corresponding to a temperature of absolute zero. The unit of temperature on this scale is the degree Celsius (°C)(°C). Thermometers measure temperature according to well-defined scales of measurement. If you are redistributing all or part of this book in a print format, The freezing and boiling temperatures of water at standard atmospheric pressure are commonly used. This property is the basis for the common alcohol thermometer and the original mercury thermometers. As will be discussed in the section on phase changes, the coexistence is achieved by lowering the pressure and consequently the boiling point to reach the freezing point. The three most common temperature scales are Fahrenheit, Celsius, and Kelvin. The definition of temperature in terms of molecular motion suggests that there should be a lowest possible temperature, where the average kinetic energy of molecules is zero (or the minimum allowed by quantum mechanics). When the temperature around the glass tube increases, the liquid starts to expand in the tube. When the thermometer’s temperature increases, the liquid from the bulb is forced into the narrow tube, producing a large change in the length of the column for a small change in temperature. Therefore, a standard thermometer is required. Scientists and doctors have created a wide variety of thermometer which can be used to measure the body temperature. © 1999-2020, Rice University. The OpenStax name, OpenStax logo, OpenStax book If the results are extrapolated to zero density, the results agree quite well, with zero pressure corresponding to a temperature of absolute zero. This is not the latest thermometer that has been developed. The Fahrenheit scale (still the most frequently used for common purposes in the United States) has the freezing point of water at \(32^o F\) and the boiling point a. Substitute the known value into the equation and solve: Similarly, we find that TK=TC+273.15=298KTK=TC+273.15=298K. Constant-volume gas thermometers are big and come to equilibrium slowly, so they are used mostly as standards to calibrate other thermometers. If you have a digital thermometer, it will make a beeping noise once the reading is complete. Thus 0 K is absolute zero. Creative Commons Attribution License 4.0 license. How To Measure Body Temperature By Thermometer? These are used in case of babies that are older than 3 months, and this thermometer requires a couple of minutes to provide you with an accurate reading. This property is the basis for the common alcohol thermometer and the original mercury thermometers. Want to cite, share, or modify this book? On the other hand, Alcohol is not used when it comes to measuring high temperature as it starts to boils at 80 degrees Celsius. We recommend using a Why are Children not given a thermometer to put in their mouth? Then our farther brings up the ultimate testing weapon, the thermometer, and all our dreams of having a rest day from school went up in smoke. The SI temperature unit is the kelvin, which is abbreviated K (not accompanied by a degree sign). The glass tube has a backboard inside in which the unit to measure temperature is marked. Substitute the known value into the equation and solve: \[T_F = \dfrac{9}{5}(25^oC) + 32 = 77^oF. Thus, a temperature difference of one degree on the Celsius scale is 1.8 times as large as a difference of one degree on the Fahrenheit scale, or. Below. Therefore, temperature differences are the same in units of kelvins and degrees Celsius, or \(\Delta T_C = \Delta T_K\). The definition of temperature in terms of molecular motion suggests that there should be a lowest possible temperature, where the average kinetic energy of molecules is zero (or the minimum allowed by quantum mechanics). Metrologists (experts in the science of measurement) have chosen the constant-volume gas thermometer for this purpose. The Liquid in Glass Thermometer: We have already seen that two types of liquid used for thermometer one is known as alcohol and other is mercury. As will be discussed in the section on phase changes, the coexistence is achieved by lowering the pressure and consequently the boiling point to reach the freezing point. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. These are the latest thermometers that we see today, and they are pretty convenient as you don’t even have to get in contact with the patient. You can find them in your local drug store, and they can be used both in the public and private environments. Using “TP” to represent the triple point. Otherwise, you can take it out after 50 seconds and note down the reading of liquid alongside the degrees. You can see that 100 Celsius degrees span the same range as 180 Fahrenheit degrees. It’s more of the test then a thermometer, but still, a lot of doctors considered it to be one. The Fahrenheit scale (still the most frequently used for common purposes in the United States) has the freezing point of water at 32°F32°F and the boiling point at 212°F.212°F. First, wash your hands with soap and water. The relationships between the three common temperature scales are shown in Figure 1.4. A vessel of constant volume filled with gas is subjected to temperature changes, and the measured temperature is proportional to the change in pressure. 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