Physics Heat
Heat transfers kinetic energy between mediums through conductive, convective, and radiative modes, originating from various sources.
Definition:
It is the result of the flow of kinetic energy from one media or item to another, or from a source of energy to an object or medium.
As a Form of Energy:
Since all many forms of energy, including heat, can be converted to work, the amount of energy is expressed in units of work such as joules, foot-pounds, kilowatt-hours, or calories. There are exact relationships between the amount of heat added to or removed from a body and the degree of its effect on the body's condition. The calorie and the British thermal unit (BTU) are the two heat measuring units that are most frequently used. A calorie (or gram-calorie) is the amount of energy required to raise the temperature of a gram of water from 14.5°C to 15.5°C; One BTU is the amount of energy it takes to raise the temperature of one pound of water from 63°F to 64°F. One BTU is about 252 calories. Both definitions indicate that temperature changes should be measured at a constant pressure of one atmosphere because the amount of energy involved depends in part on the pressure. The calorie used to measure the energy content of foods is the large calorie, or kilogram calorie, equal to 1000 gram calories.
Heat Transfer:
Since heat is energy in a transition state, a discussion of the mechanisms involved is in order. There are three modes of heat transfer which can be described as (1) conductive transfer in stationary solids or liquids, (2) convective transfer in moving liquids or gases, combining conduction with fluid flow, and (3) radiative transfer, which occurs without material support.
An example of thermal radiation is the effect of infrared (IR) energy when it hits a surface. IR is an electromagnetic field that can transfer energy from a source, such as a fireplace, to a destination, such as surfaces in a room. Radiation requires no intermediate medium; it can take place through a vacuum. It is responsible for heating the earth from the sun.
Thermal conduction occurs when two material media or objects are in direct contact and the temperature of one is higher than the other. Temperatures tend to even out; thermal conductivity thus consists of the transfer of kinetic energy from a hotter medium to a colder medium. An example is the immersion of a cold human body in a warm bath.
Convection heat occurs when the movement of a liquid or gas transfers energy from a hotter area to a cooler area. A good example of convection is the tendency of warm air to rise and cold air to fall, making the temperature of the air in the room the same as a hot stove. Thermal convection (along with thermal conduction) is believed to occur within the Earth, transferring kinetic energy from the inner core through the outer core and mantle to the Earth's crust. In this situation, the outer core and mantle behave like liquids for a long time.
History:
The heat flux in metal rods was studied analytically by the French mathematician Jean-Baptiste-Joseph Fourier and measured by the French physicist Jean-Baptiste Biot in 1816. The electrical conductivity of water was first determined in 1839; it was not until 1860 that the conductivity of gases was measured. Biot formulated the laws of conduction in 1804 and Fourier published a mathematical description of this phenomenon in 1822. In 1803 it was discovered that infrared rays are reflected and refracted like visible light, and from then on the study of thermal radiation became part of the study of radiation in general. In 1859, German physicist Gustav Robert Kirchhoff introduced his radiation law that related the power of radiation to absorption. The link between the energy emitted by a black body and the fourth power of its temperature was discovered by Austrian Josef Stefan and is today known as the Stefan-Boltzmann law. Ludwig Boltzmann laid the mathematical foundations for this radiation law in 1884. It was during the study of radiation that Max Planck came up with the concept of quantum. Although Sir Isaac Newton provided the equation explaining such processes in 1701, the concept of convection heat transport was only understood between 1880 and 1920.
Experiment:
Take three glasses, the first with cold water, the second with hot water, and the third with normal temperature water. If we dip our fingers into glass 1 and then into glass 3, we will see that the water in glass 3 is warm compared to the water in glass 1. However, if we dip our fingers into glass 2 and then into glass 3, we turn to note that the water in glass 3 is colder than in glass 2. This shows that we cannot rely on our sense of touch to judge whether an object is hot or cold, and therefore how hot or cold an object is measured by temperature.
Temperature is a measure of how hot or cold a body is. Celsius (C) or Fahrenheit (F) or Kelvin (K). Ratios are determined by the amount of heat added and removed from the body.
Formulas:
- H = (VI)t.
- H = (I 2 R)t.
- H = (V 2 /R)t.
Classification:
Hot:
Cold:
Difference Between Heat and temperature
Below is a table explaining heat versus temperature:
| Parameter | Heat | Temperature |
| Definition | Heat is defined as the total energy of an object in which molecular motion takes place. | Temperature is defined as a measure of the thermal energy of an object. |
| SI Unit | Joule | Kelvin |
| Symbol | Q | T |
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