All About Temperature

Every object possesses heat energy, and temperature is the measure of this energy. It is a relative measurement that uses scales based on reference points to provide accurate results. Measurement of temperature is a relatively new concept that was developed only during the 17th century. Early scientists understood the difference between “hot” and “cold”, but it was only during the invention of the thermometer that they had the means to measure temperature accurately.


What is Temperature?

Temperature is often defined as the degree of hotness or coldness of a body or an environment. In science, it denotes molecular motion and energy flow. Qualitatively, temperature is identified as the sensation of warmth or coldness that is felt upon contact with an object. Quantitatively, it is the measure of the heat energy of systems that are in thermal equilibrium. Thermal equilibrium is the condition wherein thermal changes between two objects have stopped.


The Development of Thermometers and Temperature Scales

Thermometers are devices that measure temperature with the use of a thermometric medium, which is gauged in different ways and by different scales. Thermoscopes were the earliest devices used to measure temperature. They used air and a colored liquid in a scaled tube. Alcohol replaced air as a thermometric medium. Later on, mercury replaced alcohol since its thermal expansion is uniform, and it can remain liquid for a wider range of temperatures. Gabriel Fahrenheit (1686-1736) made this discovery, and he devised his own scale for measuring temperature. This scale has been known as “Fahrenheit” ever since.

Another scale invented was the Centigrade scale. Anders Celsius (1701-1744) divided the difference between the temperatures of the boiling and freezing points of water into 100 degrees. The centigrade scale was renamed the “Celsius” scale after Celsius' death. Subsequently, gas thermometers were introduced, and this allowed scientists to determine that different gases have very little differences in the temperature scales. The Ideal Gas Law was established later, and it was based on a very simple relationship between volume, pressure, and temperature. With the Ideal Gas Law equation, there is a naturally-defined zero point on the scale, wherein pressure is zero and temperature is also zero. The other point is the triple point of water where water exists as liquid water, ice, and water vapor at the same temperature. The value was set at 273.16, and the scale was named “Kelvin”, after Lord Kelvin (1824-1907).


Heat and Thermodynamics

To understand the concept of temperature, it is important to know the first and second laws of thermodynamics. The first law states that energy is neither created nor destroyed. Energy can only change forms or can be transferred from one object to another. The second law states that heat flows spontaneously from a region of higher temperature to one of lower temperature. The reverse simply does not happen. With these laws in mind, it is easier to picture temperature as the measurement of how heat energy moves from one environment to another.


The Kinetic Theory

Temperature is further explained by the kinetic theory that states that gases are made up of microscopic particles that are in constant, random motion. These particles are moving rapidly and colliding with each other as well as the walls of their containers. Thermal energy is transferred from one body to another during these molecular collisions.


Thermal Radiation

Thermal radiation is the electromagnetic radiation that an object emits due to its temperature. When charged particles within atoms move, they generate thermal radiation that is converted to electromagnetic radiation. An example is the solar radiation that is released by the sun during the day to heat the earth.


3 K – The Temperature of the Universe

In 1965, Arno Penzias and Robert Wilson made a discovery that confirmed predictions that the temperature of the universe was at 3 K. It is believed that after the Big Bang, the enormous thermal energy that was released started cooling down as the universe expanded. The discovery was made from a carefully calibrated radio telescope, and since then, satellites have been launched to make more accurate measurements.

Temperature is an important physical concept, and the understanding of this concept allows human beings to solve many practical problems. It is a very broad concept that is intimately linked with other physical concepts such as pressure and volume.

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