physik experiment temperatur

For those of you who prefer your linear transformations in y  =  mx  +  b form, here's that last conversion again…

The only advantage to this notation is that it can be used to show that…

0 °F = −17.78 °C

Totally worth it.

Temperature, Kinetic Theory, and the Gas Laws

Temperature, learning objectives.

By the end of this section, you will be able to:

• Define temperature.
• Convert temperatures between the Celsius, Fahrenheit, and Kelvin scales.
• Define thermal equilibrium.
• State the zeroth law of thermodynamics.

The concept of temperature has evolved from the common concepts of hot and cold. Human perception of what feels hot or cold is a relative one. For example, if you place one hand in hot water and the other in cold water, and then place both hands in tepid water, the tepid water will feel cool to the hand that was in hot water, and warm to the one that was in cold water. The scientific definition of temperature is less ambiguous than your senses of hot and cold. Temperature is operationally defined to be what we measure with a thermometer. (Many physical quantities are defined solely in terms of how they are measured. We shall see later how temperature is related to the kinetic energies of atoms and molecules, a more physical explanation.) Two accurate thermometers, one placed in hot water and the other in cold water, will show the hot water to have a higher temperature. If they are then placed in the tepid water, both will give identical readings (within measurement uncertainties). In this section, we discuss temperature, its measurement by thermometers, and its relationship to thermal equilibrium. Again, temperature is the quantity measured by a thermometer.

Misconception Alert: Human Perception vs. Reality

On a cold winter morning, the wood on a porch feels warmer than the metal of your bike. The wood and bicycle are in thermal equilibrium with the outside air, and are thus the same temperature. They feel different because of the difference in the way that they conduct heat away from your skin. The metal conducts heat away from your body faster than the wood does (see more about conductivity in Conduction). This is just one example demonstrating that the human sense of hot and cold is not determined by temperature alone.

Another factor that affects our perception of temperature is humidity. Most people feel much hotter on hot, humid days than on hot, dry days. This is because on humid days, sweat does not evaporate from the skin as efficiently as it does on dry days. It is the evaporation of sweat (or water from a sprinkler or pool) that cools us off.

Figure 1. The curvature of a bimetallic strip depends on temperature. (a) The strip is straight at the starting temperature, where its two components have the same length. (b) At a higher temperature, this strip bends to the right, because the metal on the left has expanded more than the metal on the right.

Any physical property that depends on temperature, and whose response to temperature is reproducible, can be used as the basis of a thermometer. Because many physical properties depend on temperature, the variety of thermometers is remarkable. For example, volume increases with temperature for most substances. This property is the basis for the common alcohol thermometer, the old mercury thermometer, and the bimetallic strip (Figure 1).

Other properties used to measure temperature include electrical resistance and color and the emission of infrared radiation.

One example of electrical resistance and color is found in a plastic thermometer. Each of the six squares on the plastic (liquid crystal) thermometer in Figure 2 contains a film of a different heat-sensitive liquid crystal material Below 95ºF, all six squares are black. When the plastic thermometer is exposed to temperature that increases to 95ºF, the first liquid crystal square changes color. When the temperature increases above 96.8ºF the second liquid crystal square also changes color, and so forth.

Figure 2. A plastic (liquid crystal) thermometer. (credit: Arkrishna, Wikimedia Commons)

Figure 3. Fireman Jason Ormand uses a pyrometer to check the temperature of an aircraft carrier’s ventilation system. (credit: Lamel J. Hinton/U.S. Navy)

An example of emission of radiation is shown in the use of a pyrometer (Figure 3). Infrared radiation (whose emission varies with temperature) from the vent in Figure 3 is measured and a temperature readout is quickly produced. Infrared measurements are also frequently used as a measure of body temperature. These modern thermometers, placed in the ear canal, are more accurate than alcohol thermometers placed under the tongue or in the armpit.

Temperature Scales

Thermometers are used to measure temperature according to well-defined scales of measurement, which use pre-defined reference points to help compare quantities. The three most common temperature scales are the Fahrenheit, Celsius, and Kelvin scales. A temperature scale can be created by identifying two easily reproducible temperatures. The freezing and boiling temperatures of water at standard atmospheric pressure are commonly used.

The Celsius scale (which replaced the slightly different centigrade scale) has the freezing point of water at 0ºC and the boiling point at 100ºC. Its unit is the degree Celsius (ºC). On the Fahrenheit scale (still the most frequently used in the United States), the freezing point of water is at 32ºF and the boiling point is at 212ºF. The unit of temperature on this scale is the degree Fahrenheit (ºF). Note that a temperature difference of one degree Celsius is greater than a temperature difference of one degree Fahrenheit. Only 100 Celsius degrees span the same range as 180 Fahrenheit degrees, thus one degree on the Celsius scale is 1.8 times larger than one degree on the Fahrenheit scale 180/100=9/5.

The Kelvin scale is the temperature scale that is commonly used in science. It is an absolute temperature scale defined to have 0 K at the lowest possible temperature, called absolute zero . The official temperature unit on this scale is the kelvin , which is abbreviated K, and is not accompanied by a degree sign. The freezing and boiling points of water are 273.15 K and 373.15 K, respectively. Thus, the magnitude of temperature differences is the same in units of kelvins and degrees Celsius. Unlike other temperature scales, the Kelvin scale is an absolute scale. It is used extensively in scientific work because a number of physical quantities, such as the volume of an ideal gas, are directly related to absolute temperature. The kelvin is the SI unit used in scientific work.

Figure 4. Relationships between the Fahrenheit, Celsius, and Kelvin temperature scales, rounded to the nearest degree. The relative sizes of the scales are also shown.

The relationships between the three common temperature scales is shown in Figure 4. Temperatures on these scales can be converted using the equations in Table 1.

Notice that the conversions between Fahrenheit and Kelvin look quite complicated. In fact, they are simple combinations of the conversions between Fahrenheit and Celsius, and the conversions between Celsius and Kelvin.

Example 1. Converting between Temperature Scales: Room Temperature

“Room temperature” is generally defined to be 25ºC.

• What is room temperature in ºF?
• What is it in K?

To answer these questions, all we need to do is choose the correct conversion equations and plug in the known values.

Solution for Part 1

• Choose the right equation. To convert from ºC to ºF, use the equation [latex]T_{^{\circ}\text{F}}=\frac{9}{5}T_{^{\circ}\text{C}}+32\\[/latex].
• Plug the known value into the equation and solve: [latex]T_{^{\circ}\text{F}}=\frac{9}{5}25{^{\circ}\text{C}}+32=77^{\circ}\text{F}\\[/latex]

Solution for Part 2

• Choose the right equation. To convert from ºC to K, use the equation  T K =  T ºC  + 273.15
• Plug the known value into the equation and solve:  T K = 25ºC + 273.15 = 298 K.

Example 2. Converting between Temperature Scales: the Reaumur Scale

The Reaumur scale is a temperature scale that was used widely in Europe in the eighteenth and nineteenth centuries. On the Reaumur temperature scale, the freezing point of water is 0ºR and the boiling temperature is 80ºR. If “room temperature” is 25ºC on the Celsius scale, what is it on the Reaumur scale?

To answer this question, we must compare the Reaumur scale to the Celsius scale. The difference between the freezing point and boiling point of water on the Reaumur scale is 80ºR. On the Celsius scale it is 100ºC. Therefore 100º C=80ºR. Both scales start at 0 º for freezing, so we can derive a simple formula to convert between temperatures on the two scales.

• Derive a formula to convert from one scale to the other: [latex]T_{^{\circ}\text{R}}=\frac{0.8^{\circ}\text{R}}{^{\circ}\text{C}}\times{T}_{^{\circ}\text{C}}\\[/latex]
• Plug the known value into the equation and solve: [latex]T_{^{\circ}\text{R}}=\frac{0.8^{\circ}\text{R}}{^{\circ}\text{C}}\times25^{\circ}\text{C}=20^{\circ}\text{R}\\[/latex]

Temperature Ranges in the Universe

Figure 6 shows the wide range of temperatures found in the universe. Human beings have been known to survive with body temperatures within a small range, from 24ºC to 44ºC (75ºF to 111ºF). The average normal body temperature is usually given as 37.0ºC (98.6ºF), and variations in this temperature can indicate a medical condition: a fever, an infection, a tumor, or circulatory problems (see Figure 5).

Figure 5. This image of radiation from a person’s body (an infrared thermograph) shows the location of temperature abnormalities in the upper body. Dark blue corresponds to cold areas and red to white corresponds to hot areas. An elevated temperature might be an indication of malignant tissue (a cancerous tumor in the breast, for example), while a depressed temperature might be due to a decline in blood flow from a clot. In this case, the abnormalities are caused by a condition called hyperhidrosis. (credit: Porcelina81, Wikimedia Commons)

The lowest temperatures ever recorded have been measured during laboratory experiments: 4.5 × 10 −10 K at the Massachusetts Institute of Technology (USA), and 1.0 × 10 −10 K at Helsinki University of Technology (Finland). In comparison, the coldest recorded place on Earth’s surface is Vostok, Antarctica at 183 K (–89ºC), and the coldest place (outside the lab) known in the universe is the Boomerang Nebula, with a temperature of 1 K.

Figure 6. Each increment on this logarithmic scale indicates an increase by a factor of ten, and thus illustrates the tremendous range of temperatures in nature. Note that zero on a logarithmic scale would occur off the bottom of the page at infinity.

Making Connections: Absolute Zero

What is absolute zero? Absolute zero is the temperature at which all molecular motion has ceased. The concept of absolute zero arises from the behavior of gases. Figure 7 shows how the pressure of gases at a constant volume decreases as temperature decreases. Various scientists have noted that the pressures of gases extrapolate to zero at the same temperature, –273.15ºC. This extrapolation implies that there is a lowest temperature. This temperature is called absolute zero . Today we know that most gases first liquefy and then freeze, and it is not actually possible to reach absolute zero. The numerical value of absolute zero temperature is –273.15ºC or 0 K.

Thermal Equilibrium and the Zeroth Law of Thermodynamics

Figure 7. Graph of pressure versus temperature for various gases kept at a constant volume. Note that all of the graphs extrapolate to zero pressure at the same temperature.

Thermometers actually take their own temperature, not the temperature of the object they are measuring. This raises the question of how we can be certain that a thermometer measures the temperature of the object with which it is in contact. It is based on the fact that any two systems placed in thermal contact (meaning heat transfer can occur between them) will reach the same temperature. That is, heat will flow from the hotter object to the cooler one until they have exactly the same temperature. The objects are then in thermal equilibrium , and no further changes will occur. The systems interact and change because their temperatures differ, and the changes stop once their temperatures are the same. Thus, if enough time is allowed for this transfer of heat to run its course, the temperature a thermometer registers does represent the system with which it is in thermal equilibrium. Thermal equilibrium is established when two bodies are in contact with each other and can freely exchange energy.

Furthermore, experimentation has shown that if two systems, A and B, are in thermal equilibrium with each another, and B is in thermal equilibrium with a third system C, then A is also in thermal equilibrium with C. This conclusion may seem obvious, because all three have the same temperature, but it is basic to thermodynamics. It is called the zeroth law of thermodynamics .

The Zeroth Law of Thermodynamics

If two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.

This law was postulated in the 1930s, after the first and second laws of thermodynamics had been developed and named. It is called the zeroth law because it comes logically before the first and second laws (discussed in Thermodynamics). An example of this law in action is seen in babies in incubators: babies in incubators normally have very few clothes on, so to an observer they look as if they may not be warm enough. However, the temperature of the air, the cot, and the baby is the same, because they are in thermal equilibrium, which is accomplished by maintaining air temperature to keep the baby comfortable.

Check Your Understanding

Does the temperature of a body depend on its size?

No, the system can be divided into smaller parts each of which is at the same temperature. We say that the temperature is an intensive quantity. Intensive quantities are independent of size.

Section Summary

• Temperature is the quantity measured by a thermometer.
• Temperature is related to the average kinetic energy of atoms and molecules in a system.
• Absolute zero is the temperature at which there is no molecular motion.
• There are three main temperature scales: Celsius, Fahrenheit, and Kelvin.
• [latex]T_{^{\circ}\text{F}}=\frac{9}{5}T_{^{\circ}\text{C}}+32\\[/latex]
• [latex]T_{^{\circ}\text{C}}=\frac{5}{9}\left(T_{^{\circ}\text{F}}-32\right)\\[/latex]
• T K = T ºC + 273.15
• T ºC = T K − 273.15
• Systems are in thermal equilibrium when they have the same temperature. Thermal equilibrium occurs when two bodies are in contact with each other and can freely exchange energy. The zeroth law of thermodynamics states that when two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.

Conceptual Questions

• What does it mean to say that two systems are in thermal equilibrium?
• Give an example of a physical property that varies with temperature and describe how it is used to measure temperature.
• When a cold alcohol thermometer is placed in a hot liquid, the column of alcohol goes down slightly before going up. Explain why.
• If you add boiling water to a cup at room temperature, what would you expect the final equilibrium temperature of the unit to be? You will need to include the surroundings as part of the system. Consider the zeroth law of thermodynamics.

Problems & Exercises

• What is the Fahrenheit temperature of a person with a 39.0ºC fever?
• Frost damage to most plants occurs at temperatures of 28.0ºF or lower. What is this temperature on the Kelvin scale?
• To conserve energy, room temperatures are kept at 68.0ºF in the winter and 78.0ºF in the summer. What are these temperatures on the Celsius scale?
• A tungsten light bulb filament may operate at 2900 K. What is its Fahrenheit temperature? What is this on the Celsius scale?
• The surface temperature of the Sun is about 5750 K. What is this temperature on the Fahrenheit scale?
• One of the hottest temperatures ever recorded on the surface of Earth was 134ºF in Death Valley, CA. What is this temperature in Celsius degrees? What is this temperature in Kelvin?
• (a) Suppose a cold front blows into your locale and drops the temperature by 40.0 Fahrenheit degrees. How many degrees Celsius does the temperature decrease when there is a 40.0ºF decrease in temperature? (b) Show that any change in temperature in Fahrenheit degrees is nine-fifths the change in Celsius degrees.
• (a) At what temperature do the Fahrenheit and Celsius scales have the same numerical value? (b) At what temperature do the Fahrenheit and Kelvin scales have the same numerical value?

temperature:  the quantity measured by a thermometer

Celsius scale:  temperature scale in which the freezing point of water is 0ºC and the boiling point of water is 100ºC

degree Celsius:  unit on the Celsius temperature scale

Fahrenheit scale:  temperature scale in which the freezing point of water is 32ºF and the boiling point of water is 212ºF

degree Fahrenheit:  unit on the Fahrenheit temperature scale

Kelvin scale:  temperature scale in which 0 K is the lowest possible temperature, representing absolute zero

absolute zero:  the lowest possible temperature; the temperature at which all molecular motion ceases

thermal equilibrium:  the condition in which heat no longer flows between two objects that are in contact; the two objects have the same temperature

zeroth law of thermodynamics:  law that states that if two objects are in thermal equilibrium, and a third object is in thermal equilibrium with one of those objects, it is also in thermal equilibrium with the other object

Selected Solutions to Problems & Exercises

3.  20.0ºC and 25.6ºC

7.  (a) 22.2ºC; (b)

[latex]\begin{array}{lll}\Delta T\left(^{\circ}\text{F}\right)& =& {T}_{2}\left(^{\circ}\text{F}\right)-{T}_{1}\left(^{\circ}\text{F}\right)\\ & =& \frac{9}{5}{T}_{2}\left(^{\circ}\text{C}\right)+\text{32}\text{.}0^{\circ}-\left(\frac{9}{5}{T}_{1}\left(^{\circ}\text{C}\right)+\text{32}\text{.}0^{\circ}\right)\\ & =& \frac{9}{5}\left({T}_{2}\left(^{\circ}\text{C}\right)-{T}_{1}\left(^{\circ}\text{C}\right)\right)\text{}=\frac{9}{5}\Delta T\left(^{\circ}\text{C}\right)\end{array}\\[/latex]

• College Physics. Authored by : OpenStax College. Located at : http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a/College_Physics . License : CC BY: Attribution . License Terms : Located at License

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic & molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids & bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals & rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants & mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition & subtraction addition & subtraction, sciencing_icons_multiplication & division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations & expressions equations & expressions, sciencing_icons_ratios & proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents & logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

• Share Tweet Email Print

Temperature

Thermal conductivity, phase transitions, thermodynamics.

• Home ⋅
• Science ⋅

Temperature (Physics): Definition, Formula & Examples

You may already have an intuitive sense that temperature is a measure of the "coldness" or "hotness" of an object. Many people are obsessed with checking the forecast so they know what the temperature will be for the day. But what does temperature really mean in physics?

Definition of Temperature

Temperature is a measure of average kinetic energy per molecule in a substance. It is different from heat, although the two quantities are intimately related. Heat is the energy transferred between two objects at different temperatures.

Any physical substance to which you might attribute the property of temperature is made of atoms and molecules. Those atoms and molecules do not stay still, even in a solid. They are constantly moving and jiggling around, but the motion happens on such a small scale, that you can’t see it.

As you likely recall from your study of mechanics, objects in motion have a form of energy called ​ kinetic energy ​ that is associated with both their mass and how fast they are moving. So when temperature is described as average kinetic energy per molecule, it is the energy associated with this molecular motion that is being described.

Temperature Scales

There are many different scales by which you might measure temperature, but the most common ones are Fahrenheit, Celsius and Kelvin.

The Fahrenheit scale is what those who live in the United States and a few other countries are most familiar with. On this scale water freezes at 32 degrees Fahrenheit, and the temperature of boiling water is 212 F.

The Celsius scale (sometimes also referred to as centigrade) is used in most other countries around the world. On this scale the freezing point of water is at 0 C and the boiling point of water is at 100 C.

The Kelvin scale, named for Lord Kelvin, is the scientific standard. Zero on this scale is at absolute zero, which is where all molecular motion stops. It is considered an absolute temperature scale.

Converting Between Temperature Scales

To convert from Celsius to Fahrenheit, use the following relationship:

Where ​ T ​ ​ F ​ is the temperature in Fahrenheit, and ​ T C ​ is the temperature in Celsius. For example, 20 degrees Celsius is equivalent to:

To convert in the other direction, from Fahrenheit to Celsius, use the following:

To convert from Celsius to Kelvin, the formula is even simpler because the increment size is the same, and they just have different starting values:

In many expressions in thermodynamics, the important quantity is ​ ΔT ​ (the change in temperature) as opposed to the absolute temperature itself. Because the Celsius degree is the same size as an increment on the Kelvin scale, ​ ΔT K ​ = ​ ΔT C ​, meaning these units can be used interchangeable in those cases. However, anytime an absolute temperature is required, it must be in Kelvin.

Heat Transfer

When two objects at different temperatures are in contact with each other, heat transfer will occur, with heat flowing from the object at the higher temperature to the object at the lower temperature until thermal equilibrium is reached.

This transfer occurs due to collisions between the higher-energy molecules in the hot object with the lower-energy molecules in the cooler object, transferring energy to them in the process until enough random collisions between molecules in the materials have occurred that the energy becomes equally distributed between the objects or substances. As a result, a new final temperature is achieved, which lies between the original temperatures of the hot and the cool objects.

Another way to think of this is that the total energy contained in both substances eventually becomes equally distributed between the substances.

The final temperature of two objects at different initial temperatures once they reach thermal equilibrium can be found by using the relationship between heat energy ​ Q ​, specific heat capacity ​ c ​, mass ​ m ​ and the temperature change given by the following equation:

​ Example: ​ Suppose 0.1 kg of copper pennies (​ c c ​ = 390 J/kgK) at 50 degrees Celsius are dropped into 0.1 kg of water (​ c w ​ = 4,186 J/kgK) at 20 degrees Celsius. What will the final temperature be once thermal equilibrium is achieved?

Solution: Consider that the heat added to the water from the pennies will equal the heat removed from the pennies. So if the water absorbs heat ​ Q w ​ where:

Then for the copper pennies:

This allows you to write the relationship:

Then you can make use of the fact that both the copper pennies and the water should have the same final temperature, ​ T f ​, such that:

Plugging these ​ ΔT ​ expressions into the previous equation, you can then solve for ​ T f ​. A little algebra gives the following result:

Plugging in the values then gives:

Note: If you're surprised that the value is so close to the water's initial temperature, consider the significant differences between the specific heat of water and the specific heat of copper. It takes a lot more energy to cause a temperature change in water than it does to cause a temperature change in copper.

How Thermometers Work

Old-fashioned glass-bulb mercury thermometers measure temperature by making use of the thermal expansion properties of mercury. Mercury expands when warm and contracts when cool (and to a much larger degree than the glass thermometer which contains it does.) So as the mercury expands, it rises inside the glass tube, allowing for measurement.

Spring thermometers – those that usually have a circular face with a metal pointer – also work off of the principle of thermal expansion. They contain a piece of coiled metal that expands and cools based on temperature, causing the pointer to move.

Digital thermometers make use of heat-sensitive liquid crystals to trigger digital temperature displays.

Relationship Between Temperature and Internal Energy

While temperature is a measure of the average kinetic energy per molecule, internal energy is the total of all of the kinetic and potential energies of the molecules. For an ideal gas, where potential energy of the particles due to interactions is negligible, the total internal energy ​ E ​ is given by the formula:

Where ​ n ​ is the number of moles and ​ R ​ is the universal gas constant = 8.3145 J/molK.

Not surprisingly, as temperature increases, thermal energy increases. This relationship also makes it clear why the Kelvin scale is important. The internal energy should be any value 0 or greater. It would never make sense for it to be negative. Not using the Kelvin scale would complicate the internal energy equation and require the addition of a constant to correct it. The internal energy becomes 0 at absolute 0 K.

Related Articles

Thermal conductivity: definition, units, equation &..., phase transitions: types, classifications, properties....

• Farmer's Almanac: How Does a Thermometer Work?
• The Physics Classroom: Temperature and Thermometers
• The Engineering ToolBox: Specific Heat of Some Metals

About the Author

Gayle Towell is a freelance writer and editor living in Oregon. She earned masters degrees in both mathematics and physics from the University of Oregon after completing a double major at Smith College, and has spent over a decade teaching these subjects to college students. Also a prolific writer of fiction, and founder of Microfiction Monday Magazine, you can learn more about Gayle at gtowell.com.

Find Your Next Great Science Fair Project! GO

Physicists find superconductor behavior at temperatures once thought 'impossible'

Scientists have observed an unexpected new behavior in a superconducting material. If physicists can figure out the cause, it could help them to find room-temperature superconductors.

Scientists have found a key process required for superconductivity occurring at higher temperatures than previously thought. It could be a small but significant step in the search for one of the "holy grails" of physics, a superconductor that operates at room temperature.

The discovery, made inside the unlikely material of an electrical insulator, reveals electrons pairing up at temperatures of up to minus 190 degrees Fahrenheit (minus 123 degrees Celsius) — one of the secret ingredients to the near-lossless flow of electricity in extremely cold superconducting materials.

So far, the physicists are baffled by why this is happening. But understanding it could help them find room-temperature superconductors. The researchers published their findings Aug. 15 in the journal Science .

"The electron pairs are telling us that they are ready to be superconducting, but something is stopping them," co-author Ke-Jun Xu , a graduate student in applied physics at Stanford University, said in a statement . "If we can find a new method to synchronize the pairs, we could apply that to possibly building higher temperature superconductors."

Superconductivity emerges from the ripples left in the wakes of electrons as they move through a material. At low enough temperatures, these ripples draw atomic nuclei to each other, in turn causing a slight offset in charge that attracts a second electron to the first.

Normally, two negative charges should repel each other. But instead, something strange happens: the electrons become bound together into a "Cooper pair."

Related: space .com/ satellites -re-entering-magnetosphere-effects-study" style="text-decoration: underline; box-sizing: border-box;">Debris from burning satellites could be affecting Earth's magnetic field

Get the Space.com Newsletter

Breaking space news, the latest updates on rocket launches, skywatching events and more!

Cooper pairs follow different quantum mechanical rules than those of lone electrons. Instead of stacking outward in energy shells, they act like particles of light, an infinite number of which can occupy the same point in space at the same time. If enough of these Cooper pairs are created throughout a material, they become a superfluid, flowing without any loss of energy due to electrical resistance.

The first superconductors, discovered by Dutch physicist Heike Kamerlingh Onnes in 1911, transitioned into this zero electrical resistivity state at unimaginably cold temperatures — near absolute zero (minus 459.67 F, or minus 273.15 C). Yet, in 1986, physicists found a copper-based material, called a cuprate, which becomes a superconductor at a much warmer (but still very cold) minus 211 F (minus 135 C).

Physicists hoped this discovery would lead them to room-temperature superconductors. Yet insights into what causes cuprates to display their unusual behavior slowed and, last year, viral claims of viable room-temperature superconductors ended in allegations of data falsification and disappointment .

To investigate further, the scientists behind the new research turned to a cuprate known as neodymium cerium copper oxide. This material's maximum superconducting temperature is relatively low at minus 414.67 F (minus 248 C), so scientists haven't bothered to study it much. But when the study researchers shone ultraviolet light onto its surface they observed something strange.

— Watch Chinese researchers test out new Mars and moon rover tech (video)

— NASA may use lasers to livestream from the moon one day

— Roller coaster tech could help NASA’s Artemis moon astronauts in case of a launch emergency

Usually, when packets of light, or photons, strike a cuprate which carries unpaired electrons, the photons give the electrons enough energy to be ejected from the material, causing it to lose a lot of energy. But electrons in Cooper pairs can resist their photonic eviction, causing the material to lose only a little bit of energy.

Despite its zero resistance state occurring only at very low temperatures, the researchers found that the energy gap persisted in the new material up to 150 K, and that the pairing was, bizarrely, the strongest in the most samples best at resisting the flow of electrical current.

This means that, even though the cuprate is unlikely to reach room temperature superconductivity, it could contain some hints in finding a material that can.

"Our findings open a potentially rich new path forward. We plan to study this pairing gap in the future to help engineer superconductors using new methods," senior author Zhi-Xun Shen, a professor of physics at Stanford, said in the statement. "On the one hand, we plan to use similar experimental approaches to gain further insight into this incoherent pairing state. On the other hand, we want to find ways to manipulate these materials to perhaps coerce these incoherent pairs into synchronization."

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like weird animals and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

Quantum data beamed alongside 'classical data' in the same fiber-optic connection for the 1st time

An 8,000-ton problem: How to combat space debris

SpaceX delays Polaris Dawn astronaut launch to Aug. 28 due to helium leak

Most Popular

• 2 SpaceX Polaris Dawn astronauts will conduct high-flying research in Earth orbit
• 3 Blue Origin's next space tourism flight will launch on Aug. 29
• 4 Mattel rolling out Matchbox toy of SpaceX's Tesla astronaut transport
• 5 SpaceX fires up Falcon 9 rocket ahead of Polaris Dawn astronaut launch (photos)

• Anmelden / Registrieren
• Administration
• Profil bearbeiten

Internet Explorer wird nicht von der PhET Website unterstützt. Wir empfehlen einen modernen Browser wie z.B. Chrome, Firefox oder Edge.

Physical Review B

Covering condensed matter and materials physics.

• Collections
• Editorial Team

High-temperature observation of intralayer, interlayer, and Rydberg excitons in bulk van der Waals alloy single crystals

Pravrati taank, asif ali, aravind raji, ajay k. poonia, matthew c. beard, ravi shankar singh, and k. v. adarsh, phys. rev. b 110 , 075205 – published 26 august 2024.

• No Citing Articles
• Supplemental Material
• INTRODUCTION
• RESULTS AND DISCUSSION
• CONCLUSIONS
• ACKNOWLEDGMENTS

Transition metal dichalcogenides exhibit remarkable optical properties due to the diverse number of strongly bound excitons, which can be fine-tuned by alloying. Despite a flurry of research activity in characterizing these excitons, a comprehensive and profound understanding of their behavior with temperature is lacking. Here, we report the rich spectrum of excitonic features within bulk van der Waals alloy Mo 0.5 W 0.5 S 2 and Mo 0.5 W 0.5 Se 2 single crystals through temperature-dependent reflectance spectroscopy and first-principles calculations. We observed Rydberg excitons and interlayer excitons in both the single crystals. Notably, we provide the first experimental evidence of highly energetic A ′ and B ′ excitons in Mo 0.5 W 0.5 S 2 at room temperature. The strong carrier-phonon scattering significantly broadens the A ′ ,   B ′ , and interlayer excitons at room temperature in bulk Mo 0.5 W 0.5 S 2 single crystal compared to its selenide. Our findings, supported by density functional theory and Bethe-Salpeter equation calculations, signify the crucial role of carrier-phonon interactions. These results open pathways for next-generation optoelectronic devices and quantum technologies operating at high temperature.

• Received 4 February 2024
• Revised 26 July 2024
• Accepted 29 July 2024

DOI: https://doi.org/10.1103/PhysRevB.110.075205

©2024 American Physical Society

Physics Subject Headings (PhySH)

• Research Areas
• Physical Systems

Authors & Affiliations

• 1 Department of Physics, Indian Institute of Science Education and Research Bhopal , Bhopal 462066, India
• 2 Chemistry & Nanoscience Center, National Renewable Energy Laboratory , Golden, Colorado 80401, USA
• * Contact author: [email protected]
• † Contact author: [email protected]

Article Text (Subscription Required)

Supplemental material (subscription required), references (subscription required).

Vol. 110, Iss. 7 — 15 August 2024

Access Options

• Buy Article »
• Log in with individual APS Journal Account »
• Log in with a username/password provided by your institution »
• Get access through a U.S. public or high school library »

Authorization Required

Other options.

• Buy Article »
• Find an Institution with the Article »

Download & Share

Electronic band structure using DFT and G 0 W 0 calculations of bulk (a)  Mo 0.5 W 0.5 S 2 and (b)  Mo 0.5 W 0.5 Se 2 , (panel 1). The gray dashed line illustrates the Fermi levels. Panel 2 shows the calculated total DOS and panel 3 shows the room temperature experimental valence band spectra from x-ray photoemission spectroscopy for both single crystals.

Reflectance spectrum at 80 K for bulk (a)  Mo 0.5 W 0.5 S 2 and (b)  Mo 0.5 W 0.5 Se 2 single crystals. The blue, pink, and green regions show the interlayer (IX), A ′ , and B ′ excitons, respectively. The theoretical absorption spectrum calculated using BSE for bulk (c)  Mo 0.5 W 0.5 S 2 and (d)  Mo 0.5 W 0.5 Se 2 . (e) The first derivative of the experimentally measured reflectance spectrum and the second derivative of the theoretically calculated BSE absorption spectrum of bulk Mo 0.5 W 0.5 S 2 single crystal at 80 K. The peaks represent the Rydberg excitons up to 4 s states, which follow Bohr's atomic model as shown schematically. Where blue and yellow balls are the nucleus (hole here) and the electron, respectively. The theoretical absorption spectra have been shifted by ∼ 0.26  eV for better comparison with the experimental spectra. (f) Experimentally and theoretically obtained transition energies of the Rydberg series as a function of quantum number ( n ). The n = 3 and 4 peaks follow the 3D hydrogen model and the fit is represented by the gray line. The black dashed line and the pink shaded area show the estimated E g and the uncertainty in the E g value, respectively. (g) Calculated dielectric constants ε n as a function of n . (h) The second derivative of the reflectance spectrum of bulk Mo 0.5 W 0.5 Se 2 single crystal at 4 K shows the Rydberg series up to n = 3 .

(a) Spatial distribution of excitons shows the nature of A (intralayer) and IX excitons for Mo 0.5 W 0.5 S 2 (top panel) and Mo 0.5 W 0.5 Se 2 (bottom panel). Reflectance spectra as a function of temperature for bulk (b)  Mo 0.5 W 0.5 S 2 and (c)  Mo 0.5 W 0.5 Se 2 single crystals.

Sign up to receive regular email alerts from Physical Review B

• Forgot your username/password?
• Create an account

Article Lookup

Paste a citation or doi, enter a citation.

NTRS - NASA Technical Reports Server

Available downloads, related records.