Heat, temperature, thermal expansion

Introduction

Heat and temperature are concepts that we all understand.

Temperature is a measurement of a body’s ‘ hotness. A kettle filled with boiling water is hotter than an icebox.

We need to define the terms “heat,” “temperature,” and “thermal expansion” in physics with greater care. You will discover what these are in this article.

Heat

Heat transfer is moved to or from a thermodynamic system without using thermodynamic work or matter transfer. The following portion of this article discusses the numerous modes of energy transfer that characterize heat.

Heat transmission, like thermodynamic work, is a multi-system process rather than a feature of a single system. In physics, energy transported as heat leads to changes in the cardinal energy variable of the system’s state, such as internal energy or enthalpy. This is not to be confused with the common understanding of heat as a quality of an isolated system.

The entire amount of energy moved in a process, minus any thermodynamic work done, and any energy contained in the substance carried, is the quantity of energy conveyed as heat. It is required for the proper definition of heat that it occurs by a route in which no matter is transferred.

Temperature

Temperature is a numerical expression of how hot or cold something is. Thermal energy, which is present in all matter and is the source of the occurrence of heat, a flow of energy, is manifested when a body comes into contact with another that is colder or hotter.

The temperature is measured with a thermometer. The temperature has traditionally been defined using a number of reference points and thermometric substances, and thermometers are calibrated in a variety of temperature scales.

 The Celsius scale (previously known as centigrade, designated as °C), the Fahrenheit scale (denoted as °F), and the Kelvin scale (abbreviated as K) are the most widely used. Under the International System of Units’  (SI unit) norms, the Kelvin scale (abbreviated as K) is largely used for scientific reasons.

Absolute zero is the lowest theoretical temperature at which a material cannot absorb any more thermal energy. It can only be approached very closely (100 pK), but it is impossible to achieve in trials. This is acknowledged by the third thermodynamics law.

Temperature is significant in chemistry, physics, astronomy, earth science, biology, medicine, material science, ecology, mechanical engineering, metallurgy, and geography, as well as most elements of everyday life.

Thermal Expansion

The ability of matter to change its form, area, volume, and density in reaction to a change in temperature is known as thermal expansion. Transitions between phases are not included.

The temperature has a monotonic effect on a material’s average molecular kinetic energy. When a solid is heated, the atoms begin to vibrate and move more, increasing the space between them. Materials that contract as the temperature rises are rare and only occur in a few temperature ranges. The material’s coefficient of linear thermal expansion, which varies with temperature, is the relative expansion (also known as strain) divided by the change in temperature. Particles travel faster as their energy rises, eliminating intermolecular interactions and allowing the material to expand.

LINEAR EXPANSION

In solid, thermal expansion takes place in the form of an increase in length. For example, if we consider the rod of length l to increase due to increased temperature. The linear expansion is given by

ΔL = 𝛼L ΔT L

where,

• ΔL illustrates the difference in length 
• 𝛼L is defined as the linear coefficient of thermal expansion
• In the CGS unit, the linear coefficient is represented by celsius.
• In the SI unit, the linear coefficient ‘a’ is represented by kelvin.

Area Expansion

The thermal area expansion coefficient links a change in temperature to a change in the area dimensions of a substance. The fractional change in area per degree of temperature change is what this term refers to. Without regard for the pressure, we may write:

Coefficient

Areal expansions are expressed through coefficients, which is the fractional change in area per degree of temperature change. Therefore, the coefficient denotes the rate of change of area per unit degree change in temperature.

The formula is expressed as ΔA = 2αAAΔT

Volume Expansion

We may express the volumetric (or cubical) thermal volume expansion coefficient as follows, ignoring the effects of pressure on a solid:

The formula is expressed as ΔV = βV1 ΔT

Wherein:

• V1 is the initial volume,
• ΔT is the temperature change,
• ΔV is the increase in volume,
• β is the coefficient of volumetric expansion.

Conclusion

Heat is a type of energy that moves between a body and its surrounding medium due to a temperature differential. Temperature is a numerical representation of the degree of hotness of a body.

A temperature-measuring instrument (thermometer) makes use of a quantifiable characteristic that changes with temperature (the thermometric property). Temperature scales fluctuate depending on which thermometer is used. To make a temperature scale, two fixed locations are chosen and given arbitrary temperature values. The scale’s origin and unit size are determined by these two integers.

Thermal expansion, which does not include phase changes, is the tendency of matter to alter its form, area, volume, and density in response to a change in temperature.