In our daily life, we note that a utensil placed on fire appears hot when we touch it. A piece of ice taken in hands appears cold. If steam is passed in water then it becomes warm. When one end of the metal rod is kept in fire the other end of it becomes hot after some time. Have you ever wondered about the causes of the above facts? The answer lies in knowing the thermal properties of matter which involves the study of heat and temperature. In this article, we are going to learn about what heat and temperature are and how are they measured.
Daniel Gabriel Fahrenheit
Daniel Gabriel Fahrenheit was a physicist, inventor, and builder of scientific instruments who lived from May 24, 1686, until September 16, 1736. Daniel Gabriel Fahrenheit, a Dutch scientist, and inventor produced the first dependable thermometer in 1714, utilizing mercury instead of alcohol and water combinations.
He proposed a temperature scale in 1724, which is currently (slightly adjusted) named after him. He was able to do so because he was the first to make thermometers using mercury (which has a high coefficient of expansion), and the quality of his production allowed for a finer scale and more reproducibility, resulting in widespread acceptance.
What is Heat?
We know that everybody is made up of a large number of tiny particles called molecules. Depending on the nature of the substance (solid, liquid, and gas) and its temperature, the molecule may possess translation motion i.e., motion along a straight line, vibrational motion i.e., to and fro motion about the mean position of the molecules, and rotational motion i.e., rotation of the molecules about their axes.
Every type of motion provides some kinetic energy to the molecules and hence to the body. In fact, heat possessed by a body is the total thermal energy of the body which is the sum of kinetic energies of all the individual molecules of the body due to the translational, vibrational, and rotational motion of the molecules. We know that a hot cup of tea if left on the table then it cools down and ice-cold water if left on the table it warms up. In both cases, heat is transferred from one body at a higher temperature to another body at a lower temperature. Thus heat is a form of energy that is transferred from one body at a higher temperature to another body at a lower temperature when they are placed in contact with each other. The SI unit of heat is the joule.
What is the Temperature?
Often, we confuse temperature with heat but the concept of temperature is different from the concept of heat. Generally, we define the temperature of a body as the degree of hotness or coldness of the body. When two bodies at different temperatures are kept in contact with each other then the heat flows from a body at a higher temperature to a body at a lower temperature, till their temperatures become equal. Therefore, redefining the temperature of a body as the thermal state or condition of the body, which would determine the direction of flow of heat when this body is placed in contact with another body.
Different Types of Temperature Scales
For quantitative measurement of temperature we use thermometers. A thermometer calibrated for a temperature scale is used to measure the value of a given temperature on that scale. In order to define any standard temperature scale, for the measurement of temperature, two reference points are needed, for which the physical phenomena that always occur at the same temperature. The two convenient fixed reference points are the ice point and the steam point of water at standard pressure which are known as the freezing point and boiling point of water at standard pressure. The following temperature scales are;
Celsius Temperature Scale:
It is formally known as the centigrade temperature scale and it is designed by Andre Celsius in the year 1741. Here the freezing point of ice at standard pressure is regarded as 0 oC and the boiling point of water at standard pressure as 100 oC. The space between these two fixed points is divided into 100 equal parts and each part represents 1 oC.
Fahrenheit Temperature Scale:
It was designed by Gabriel Fahrenheit in the year 1717. Here the freezing point of ice at standard pressure is regarded as 32 oF and the boiling point of water at standard pressure is 212 oF. The space between these two fixed points is divided into 180 equal parts and each part represents 1 oF. If tC and tF are temperature values of a body on the Celsius temperature scale and Fahrenheit temperature scale respectively then we can write,
Kelvin Temperature Scale:
In science, the Kelvin scale is the most widely used temperature scale. It's an absolute temperature scale with 0 K at absolute zero, or the coldest temperature imaginable. Water's freezing and boiling points are 273.15 K and 373.15 K on this scale, respectively. Unlike other temperature measures, the Kelvin scale is absolute.
Different Types of Temperature Measurement Devices
In today’s world, the temperature is measured by various types of thermometers with different types of thermometer units of measurement such as Celsius, Fahrenheit, and Kelvin. Some of these are explained below;
The mercury thermometer was created by Gabriel Fahrenheit in 1974.The stem of a mercury thermometer is a long, thin, and uniform glass tube. On the stem are indicated the scales that are used to gauge temperature. At the end of the stem, there is a little bulb that holds mercury. When a thermometer comes into touch with a heated body, mercury expands in a capillary tube inside the glass stem.
Thermometers like this may be found in homes, clinics, and hospitals. These thermometers have a kink in them that prevents the mercury from returning to the patient's mouth when it is removed, making it easier to record the temperature. On either side of the mercury thread are two temperature scales, one in Celsius and the other in Fahrenheit.It can produce temperatures ranging from 35oC(94oF) to 42oC(108oF). The Celcius scale is more sensitive than the Fahrenheit scale. As a result, the temperature is expressed in degrees Fahrenheit (°F).
Laboratory thermometers can be used in school laboratories or other labs for scientific study to keep track of the temperature. In industries, these are also used to measure the temperature of solutions or instruments. When compared to a clinical thermometer, the stem and bulb of a laboratory thermometer are longer. There is no kink in a scientific thermometer. It only has a temperature scale in Celsius. It can withstand temperatures ranging from -10oC to 110oC.
Thermocouples are voltage devices that use a change in voltage to indicate temperature measurement. The output voltage of the thermocouple rises as the temperature rises, but not always linearly.
The thermocouple is frequently enclosed in a metal or ceramic shield to protect it from a range of conditions. Many types of outer coatings, such as Teflon, are available for trouble-free usage in acids and strong caustic solutions on metal-sheathed thermocouples.
Silicon Diode Sensors
A silicon diode sensor is a gadget that was created specifically for use at cryogenic temperatures. In essence, they are linear devices in which the diode's conductivity grows linearly in low cryogenic regions.
Water was used instead of mercury in the first thermometers invented. Because water freezes at 32 degrees Fahrenheit (0 degrees Celsius), the inventors turned to mercury and alcohol.
Thermometers that used liquids worked on a straightforward principle. When the liquid was heated, it expanded, indicating a temperature increase.
In this article, we studied the concept of heat and learned the difference between heat and temperature. We discussed different temperature-measuring scales along with different temperature-measuring instruments. Different thermometers, thermocouples, and digital thermometers are used to measure temperature. Thermometers can have mercury or any other liquid in them. The expansion of mercury is exactly proportional to temperature. The expansion of fluid occurs as the temperature rises. As a result, the volume of fluid can be used to determine the temperature.