Heat : Introduction and Classification

According to heat definition, it is one of the essential forms of energy for the survival of life on earth. Transfer of heat takes place from one body to another due to difference in temperature as per thermodynamics. We use heat energy for various activities like cooking, ironing, transportation, recreation, etc. This form of energy also plays a vital role in nature. The occurrence of the wind, rain, change of seasons, etc. are dependent on the gradient created due to uneven heating of different regions. In this article, let us learn what is heat and its classification.

What is Heat?

With the increase in the temperature of a body, the vibrations of molecules or atoms increase. These vibrations are then transferred from one part of the body to another. The measure of energy with which the molecules vibrate in a system is termed as heat stored in that object.

As per the definition of heat, it is defined as the flow of energy from a warm to a cooler object. The direction of flow of the heat energy takes from the substance of higher temperature to the substance of lower temperature. This is because the molecules are vibrating faster and transfer their energy to the molecules vibrating slower. The vibrational energy is also termed as its heat content. The heat content in the body makes it hot or cold. Greater the heat content, hotter will be the body.

A substance may absorb heat without an increase in temperature by changing from one physical state to another. In the process of melting,  the substance is changed from solid to liquid. In the process of sublimation, solid is converted into the vapour state. In the process of boiling, the liquid is converted to vapour. Heat is a form of energy that can be converted into work. Amount of energy is expressed in units of work. It is expressed in joules, foot-pounds, kilowatt-hours, or calories.

Heat as a form of energy can be converted to other forms of energy. For example, in motorized vehicles, heat is converted to mechanical energy. In electric bulbs, it is converted to light energy. In thermal power plants, it is finally converted to electrical energy.

Heat - Cold

Let us take three beakers, first with cold water, the second with hot and the third with water at normal temperature. If we dip our finger in beaker 1 and then in beaker 3, we will observe that water in beaker 3 is hot as compared to that in beaker 1. Whereas, if we dip our fingers in beaker 2 and then in beaker 3, we will observe that the water in beaker 3 is colder as compared to that in beaker 2. This shows that we cannot rely on our sense of touch to judge the hotness or coldness of something and that’s why the degree of hotness or coldness of any object is measured in terms of temperature.

Temperature is the measure of hotness or coldness of the body. Celsius (C) or Fahrenheit (F) scale, or in Kelvins (K). Relations are established on the amount of heat added to taken out from the body.

Heat Transfer Occurs By Three Mechanisms: 

Conduction: It is the method in which the transfer of heat takes place between atoms and molecules in direct contact.

Convection: It is the method in which the transfer of heat happens by the movement of the heated substance.

Radiation: It is the method in which the transfer of heat takes place by electromagnetic waves.

Classification of Heat 

Heat can be classified as follows:

  • Hot
  • Cold

Hot

Objects with high heat content are defined as hot (Hotness or coolness of an object is a relative term is always measured with respect to a reference object).

Examples of hot objects around us include the sun, fire, hot pans, air from a hairdryer, lava from volcanic eruptions, etc.

Cold

Objects with lower heat content are defined as cold objects. Hotness or coolness of an object is a relative term that is always measured with respect to a reference object.

Examples of cold objects around us include ice, air from an air conditioner, cold drinks, metal vessels kept in open on cold winter days etc.

Sources of Heat

There are many sources of heat but the following are the main sources of heat:

  • Sun
  • Chemical
  • Electrical
  • Nuclear

Difference Between Heat and Temperature

Following is the table explaining heat vs temperature:

Parameter Heat  Temperature 
Definition  Heat is defined as the total energy of an object that has molecular motion inside it Temperature is defined as the measure of the thermal energy of an object
SI Unit Joule  Kelvin 
Symbol

Frequently Asked Questions – FAQs

What is temperature?

Temperature is the measure of hotness or coldness of the body.

What is the SI unit of heat?

Joule

What is the SI unit of temperature?

Kelvin

What are the sources of heat?

Following are the sources of heat:

  • Sun
  • Chemical
  • Electrical
  • Nuclear

How is heat classified?

Heat is classified into:

  • Hot
  • Cold

To know what is heat, stay tuned with BYJU’S for more such interesting articles. Also, register to “BYJU’S – The Learning App” for loads of interactive, engaging Physics-related videos and an unlimited academic assist.

2 Comments

  1. Wow, nice

  2. Thank you sir it helps me very much.

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