Introduction
We all have common- sense notions of heat and temperature. Temperature is a measure of 'hotness' of a body. A kettle with boiling water is hotter than a box containing ice. In physics, we need to define the notion of heat, temperature etc., more carefully. In this article, you will learn what is heat is and how it measured, and study the various processes by which heat flows from one body to another. Along the way, you will find out why blacksmiths heat the iron ring before fitting on the rim of a wooden wheel of a bullock cart and why the wind at the beach often reverses direction after the sun goes down.
You will also learn what happens when water boils or freezes, and it's temperature does not change during these processes even through a great deal of heat is flowing into or out of it.
Temperature and Heat
We can begin studing thermal properties of matter with definition of temperature and heat. Temperature is a relative measure, or indication of hotness or coldness. A hot utensil is said to have a high temperature, and ice cube to have a low temperatures. An object is said to be hotter. Note that hot and cold are relative terms, like tall and short. We can perceive temperature by touch.
However this temputure sense is somewhat unreliable and its range is too limited to be useful for scientific purpose.
We know from experience that a glass of ice- cold water left on a table on a hot summer day eventually warms up whereas a cup of hot tea ☕ on the same table cools down.
It means that when the temperature of body, ice-cold water or hot tea in this case, and it's surroundings medium are different, heat transfer takes place between the system and the surrounding medium, until the body and the surrounding medium are at the same temperature.
We also know that case of glass tumble of ice cold, heat flows from the environment to the tumbler, whereas in the case of hot tea, it flows from the cup of hot tea to the environment. So, we can say that heat is the form of energy transfferred between two (or more) system or a system and it's surroundings by virtue of temperature difference.
- The SI unit of heat energy transferred is expressed in joule (J) while SI unit of temperature is Kelvin (K), and C is a commonly used of temperature. When an object is heated, many changes may take place. Its temperature may rise, it may expand or change state.
