What Is Heat Energy?
Heat is a form of energy which is transferred from a substance having a higher temperature to a substance having a lower temperature. The addition of heat to a substance increases its internal temperature. Heat is defined as the net amount of thermal energy of a system.
Heat energy is produced due to the motion of subatomic particles like atoms, ions, and molecules to solids, gases, and liquids. Heat transfer occurs from one system to another system due to the temperature difference between the two systems.
(Image will be Updated soon)
All forms of matter contain heat energy. No matter if it is a volcano or an ice cube, it has some amount of heat.
Sources of Heat
There are different forms of energy in nature like mechanical energy, sound energy, light energy, electric energy, tidal energy, heat energy, etc. Heat energy is generated due to the transfer of heat from a warm system to a cool system. Heat energy is an essential form of energy in our day-to-day activities like cooking, heating, ironing, etc. An object or system from which heat energy is obtained is called a source of heat energy. Here are some of the major sources of heat energy which are mentioned below:
Sun – The living source of energy
Every second of every day the Sun gives us life generating energy towards Earth, firing our planet with light and life. We cannot always see it. Energy is everywhere you look, it's locked in the atoms giving inside things and it keeps the heart pumping blood through your veins. Energy is the only thing that drives every living things to survive.
Anything that happens from pin drop to an explosion requires energy. Energy is the capacity for doing work. Various forms of energy exist in various forms. The law of conservation of energy states that the total amount of energy in the universe is fixed; it means that energy can only change from one form to another
Earth
The heat energy which is obtained from Earth is called geothermal energy. It can be found in hot water and rocks present underground. Heat is also found in the form of molten rocks and magma, deep inside the Earth's crust.
Air
Air is also an important source of heat energy. It is used for heat pumps for both commercial and residential purposes.
Burning Fuels
Burning of fuels provides heat energy. Fuel is an energy filled combustible substance, which when burnt generates energy. Wood, coal, kerosene, gasoline, petrol, diesel, oil, and charcoal are some common fuels.
Electricity
Electric energy can be converted into heat energy. Iron, water heater, and induction cooker are some of the devices which convert electrical energy into heat energy. This is based on the principle of heating effect of electric current.
How does Heat Energy Get Transferred?
There are three ways for the transfer of heat, and they are mentioned below:
1. Convection- It is a process of heat transfer which occurs due to the actual motion of the particles. It usually occurs in liquids and gases. When air gets heated, it becomes hot and carries heat energy.
Warm air has less density as compared to cool air, hence warm air rises above and cool air descends below to fill the space. This cool air further becomes warm and rises. This process continues and produces convection current.
(Image will be Updated soon)
2. Conduction- It is the process of heat transfer which occurs due to the vibration of the molecules about their mean position.
Conduction occurs from one part of a system to another part, or in two systems which are in contact with each other. Due to closely packed molecules, solids conduct heat better than liquids and gases.
(Image will be Updated soon)
3. Radiation- It is a method of heat transfer which uses electromagnetic waves (infrared waves) to transfer heat from one place to the other.
This process does not require any medium to transfer heat. Hot objects radiate out heat waves in all directions at the speed of light. When heat waves strike with an object, it either reflects or absorbs the wave.
(Image will be Updated soon)
Heat Energy Examples
If the constituent particle of an object becomes excited by gaining energy, the particle moves or vibrates rapidly and the object is said to be hot.
If the particles have less energy, it will not vibrate, and the object is said to be cold. Heat is the transfer of energy between these objects due to a difference in temperature.
Here are some examples of heat energy:
The Sun is the biggest source of heat energy in our solar system. It radiates heat, which reaches Earth in the form of radiation.
A stovetop acts as a source of heat energy when it burns the gas. Anything which is placed above the stove also becomes a source of energy to cook things.
Automobile fuels are also a source of heat energy. When the fuel burns, it provides energy for the motion of the vehicle.
A hot cup of tea or coffee contains heat energy.
When you hold a piece of ice in your palm, the heat energy from your hand melts the ice.
A radiator, heating system, or a room heater provides the necessary radiant heat energy to warm your house during the winter season.
Conventional oven is a source of convection heat energy; the food becomes hot when it is placed in it.
Various Forms of Energy
Energy exists in many different forms. Examples of these are as follows:
light energy,
heat energy,
mechanical energy,
gravitational energy,
electrical energy,
sound energy,
chemical energy,
nuclear or atomic energy, and so on.
Each form can be converted or changed into the other forms.
Transformation of Energy
All the energy forms follow a universal law known as law of conservation of energy which states that energy can neither be created nor destroyed but can be altered from one form to the another. This implies that all forms of energy are interconvertible. The process of changing one form of energy into another is called an energy transformation.
Examples of of Converting Energy
Consider a ball falling from the top of the floor of a building. Initially, it has potential energy stored. Due to its height as the ball falls, the potential energy changes to kinetic energy.
(Image will be Updated soon)
Charging of batteries converts electrical energy to chemical energy and chemical to electrical.
(Image will be Updated soon)
Conversion of chemical energy in the form of petrol converting into heat energy and finally into kinetic energy.
Importance of Heat Energy
In physical science, heat is essential, especially for plants and animals. Plant life depends on heat, among other things, to survive as well. Heat is a result of energy, which can be beneficial as well as dangerous.
FAQs on Heat Energy
1. What exactly is heat energy and what is its SI unit?
Heat energy is the form of energy that is transferred from one body to another due to a difference in their temperatures. It always flows from a region of higher temperature to a region of lower temperature. The SI unit of heat energy is the Joule (J), the same as for any other form of energy.
2. What are some common examples of heat energy in our daily lives?
Heat energy is fundamental to many everyday activities. Some common examples include:
- The warmth we feel from the Sun, which provides light and heat to the Earth.
- Using a stove or an oven to cook food, which transfers heat to the ingredients.
- An electric iron converting electrical energy into heat to remove wrinkles from clothes.
- A room heater warming the air in a cold room.
- The heat generated by burning fuels like wood, coal, or petrol in engines and fireplaces.
3. What are the major sources of heat energy?
The primary sources of heat energy can be categorised as follows:
- The Sun: The most significant source, generating heat through nuclear fusion.
- The Earth: It provides geothermal energy from its hot core.
- Chemical Reactions: The burning (combustion) of fuels like wood, coal, and natural gas releases stored chemical energy as heat.
- Electricity: Electrical energy can be converted into heat energy due to resistance in devices like heaters and toasters, based on the principle of the heating effect of electric current.
4. What is the difference between conduction, convection, and radiation?
These are the three distinct modes of heat transfer:
- Conduction: This is heat transfer through direct contact, where thermal energy moves from particle to particle without the particles themselves moving from their position. It is most effective in solids. For example, a metal spoon getting hot when left in a cup of hot tea.
- Convection: This involves heat transfer through the actual movement of fluids (liquids or gases). Hotter, less dense fluid rises, and cooler, denser fluid sinks, creating a convection current. An example is the process of boiling water.
- Radiation: This is heat transfer through electromagnetic waves (like infrared waves) that can travel through a vacuum. It does not require any medium. An example is the heat we feel from the Sun or a campfire.
5. How is heat different from temperature?
This is a crucial concept in Physics. Temperature is a measure of the average kinetic energy of the molecules within a substance; it tells us how hot or cold an object is and is measured in Celsius, Fahrenheit, or Kelvin. In contrast, heat is the energy that is transferred from a hotter object to a colder one. An object possesses internal energy due to its temperature, but it does not 'contain' heat; heat is the energy in motion between objects.
6. Why do we feel warmer standing in direct sunlight than in the shade, even if the air temperature is the same?
This happens because of the different modes of heat transfer. The Sun transmits most of its energy to Earth via radiation. When you stand in the sun, your body absorbs this radiation directly, which makes you feel warm. When you move into the shade, you are shielded from this direct radiation. While the surrounding air (heated by convection) has the same temperature in both places, the absence of direct radiant energy in the shade makes you feel significantly cooler.
7. Is there a formula to calculate the amount of heat energy transferred?
Yes, for many situations, the amount of heat energy (Q) transferred to or from an object can be calculated using the formula: Q = mcΔT. Here, 'm' represents the mass of the substance, 'c' is its specific heat capacity (a property unique to the material), and 'ΔT' (delta-T) signifies the change in its temperature. This formula is fundamental in thermodynamics and calorimetry for the 2025-26 syllabus.
8. How does an electric heater convert electricity into heat?
An electric heater operates on the principle of the Joule heating effect. It contains a heating element, which is a resistor made of a material with high electrical resistance. When an electric current is passed through this resistor, the electrons moving through it collide with the atoms of the resistor material. These collisions cause the atoms to vibrate more vigorously, converting the electrical energy directly into heat energy, which then warms the surrounding area.
