Simply hotness may be represented abstractly, and therefore it is necessary to have an objective way of measuring temperature. It is one of the basic thermodynamic properties.
A particularly important concept is thermodynamic equilibrium. In general, when two objects are brought into thermal contact, heat will flow between them until they come into equilibrium with each other. When a temperature difference does exist, heat flows spontaneously from the warmer system to the colder system. Heat transfer occurs by conduction or by thermal radiation. When the flow of heat stops, they are said to be at the same temperature. They are then said to be in thermal equilibrium.
For example, you leave a thermometer in a cup of coffee. As the two objects interact, the thermometer becomes hotter, and the coffee cools off a little until they come into thermal equilibrium. Two objects are defined to be in thermal equilibrium if, when placed in thermal contact, no net energy flows from one to the other, and their temperatures don’t change. We may postulate:
When the two objects are in thermal equilibrium, their temperatures are equal.
This is a subject of a law that is called the “zeroth law of thermodynamics”.
For example, most materials expand when their temperature is increased. This property is very important in all of science and engineering, even in nuclear engineering. The thermodynamic efficiency of power plants changes with inlet steam temperature or even with the outside temperature. At higher temperatures, solids such as steel glow orange or even white, depending on temperature. The white light from an ordinary incandescent lightbulb comes from an extremely hot tungsten wire. It can be seen temperature is one of the fundamental characteristics that describe matter and influences matter behavior.
The kinetic theory of gases provides a microscopic explanation of temperature. It is based on the fact that during an elastic collision between a molecule with high kinetic energy and one with low kinetic energy, part of the energy will transfer to the molecule of lower kinetic energy. Temperature is therefore related to the kinetic energies of the molecules of a material. Since this relationship is fairly complex, it will be discussed later.[/su_spoiler][/su_accordion]
When using a thermometer, we need to mark a scale on the tube wall with numbers. We have to define a temperature scale. A temperature scale is a way to measure temperature relative to a starting point (0 or zero) and a unit of measurement.
These numbers are arbitrary, and historically many different schemes have been used. For example, this was done by defining some physical occurrences at given temperatures—such as the freezing and boiling points of water — and defining them as 0 and 100, respectively.
Some several scales and units exist for measuring temperature. The most common are:
- Celsius (denoted °C),
- Fahrenheit (denoted °F),
- Kelvin (denoted K, especially in science).
The temperature required nuclear fusion to occur
Deuterium-Tritium Fusion. The fusion reaction of deuterium and tritium is particularly interesting because of its potential of providing energy for the future.
3T (d, n) 4He
The reaction yields ~17 MeV of energy per reaction. Still, it requires an enormous temperature of approximately 40 million Kelvins to overcome the coulomb barrier by the attractive nuclear force, stronger at close distances. The deuterium fuel is abundant, but tritium must be either bred from lithium or gotten in the operation of the deuterium cycle.
Highest manufactured temperature
On 13 August 2012, scientists at CERN’s Large Hadron Collider (LHC), Geneva, Switzerland, announced that they created a quark-gluon plasma with a record-smashing temperature of 5.5 trillion K.
The team had been using the ALICE experiment, which is focused on studying the QCP and other conditions in the primordial Universe to smash together lead ions at 99% of the speed of light to create a quark-gluon plasma. It is believed that up to a few milliseconds after the Big Bang, the Universe was in a quark-gluon plasma state, which is an exotic state of matter. It is thought quark-gluon plasma consists of asymptotically free quarks and gluons.
Lowest manufactured temperature
According to Guinness World Records, the lowest manufactured temperature achieved is 450 picokelvin above absolute zero (only half a billionth of a degree above absolute zero). It was achieved by a team of scientists at the Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.