What is Heat of Fusion?
Heat is one of the essential energy forms on Earth for the survival of different lives. Heat transfer takes place from one body to the other because of the difference in temperature according to thermodynamics. We use heat energy in our day to day activities such as cooking, transportation, ironing, recreation and much more. Heat energy also plays a crucial role when it comes to nature. The occurrence of rain, wind, change in the seasons, etc. is all dependent on the gradient that is created because of the uneven heating of various regions. In this article, we will discuss what is meant by heat, what is Latent heat and what is used to measure heat.
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What is Heat in Science
When the temperature of a body increases, the vibrations of the atoms or molecules tend to increase. These vibrations then transfer from one part of the body to the other. The measure of the energy with which these atoms or molecules vibrate in the given system is known as the heat stored in that particular object.
According to the definition of heat, it is referred to as the flow of energy from a warmer object to a cooler object. The direction of the heat flow occurs in the substance having a higher temperature to the substance having a lower temperature. This happens because the molecules that vibrate faster transfer their energy to the molecules that vibrate slower. This vibrational energy is also called heat content. The heat content in a body makes that either hot or cold. The higher is the heat content, the hotter is the body.
A substance can even absorb heat without undergoing an increase in the temperature when it changes from one physical state to the other. During the process of melting, the substance changes from the solid-state to the liquid state. During the process of sublimation, solid tend to get converted to vapours. Heat is an energy form which can also be converted to work. Hence, the amount of energy is expressed in the same units as that of work. Energy is either expressed in terms of joules, calories, kilowatt-hours or foot-pounds.
Heat can also be converted to different other forms of energy. For example, the heat energy gets converted to the mechanical energy in a motorized vehicle. Similarly, in the electric bulbs that we use in our day to day life, the electrical energy gets converted to the light energy.
Let us consider an experiment as follows.
We will take three beakers, the first one having cold water, the second one containing hot water and the third one having water which is at the normal temperature. Now, if we dip one finger in the first beaker and then immediately into the third one, we would notice that the water in the third beaker is comparatively hotter than the previous one. If we dip our finger in the second beaker and then in the third one, we would notice that the water in the third beaker would be comparatively colder than the second one. We can therefore conclude that we cannot depend on our sense of touch for judging the level of hotness or coldness of an object. Hence, this is the reason the degree of the hotness or coldness of an object is measured in temperature.
Temperature refers to the measure of the hotness or coldness of the body. The different temperature scales are Celsius (C) scale, Fahrenheit (F) scale, or Kelvin scale (K).
Classification of Heat
Heat is classified as hot and cold.
Hot
The objects having a higher heat content are referred to as hot objects (the hotness or coldness of a given object is a relative term and hence, is always measured in regards to a reference object). Some examples of the hot objects around us are the sun, hot pans, fire, lava from the volcanic eruptions, air from the hairdryer, etc.
Cold
The objects having lower heat content are referred to as cold objects. The examples of the colder objects around us that we see are ice, cold drinks, the air from an air conditioner, etc.
FAQs on What is Heat in Physics
1. What is the primary definition of heat in physics?
In physics, heat is defined as the form of energy that is transferred from an object at a higher temperature to an object at a lower temperature. It is not a substance an object possesses, but rather energy in transit. This transfer occurs at a molecular level, where faster-vibrating particles in the hotter object pass their kinetic energy to the slower-vibrating particles in the cooler object.
2. How is heat different from temperature?
While related, heat and temperature are fundamentally different. Temperature measures the average kinetic energy of the molecules within a substance, indicating its degree of hotness or coldness. In contrast, heat is the total amount of energy transferred due to a temperature difference. For example, a tiny spark has a very high temperature, but it transfers very little heat. Conversely, a lukewarm swimming pool has a low temperature but contains a vast amount of heat energy.
3. What are the common units used to measure heat?
Since heat is a form of energy, its official SI unit is the Joule (J). However, other units are also widely used depending on the context:
- Calorie (cal): The amount of heat required to raise the temperature of one gram of water by one degree Celsius.
- British Thermal Unit (BTU): An imperial unit often used in fields like heating and air conditioning.
4. What are the three primary modes of heat transfer?
Heat moves from a hotter to a cooler place through three main processes:
- Conduction: The transfer of heat through direct physical contact, common in solids like a metal pan on a stove.
- Convection: The transfer of heat through the movement of fluids (liquids or gases), such as the circulation of boiling water or warm air rising in a room.
- Radiation: The transfer of heat via electromagnetic waves, which can travel through a vacuum. This is how the Sun's warmth reaches Earth.
5. Can you provide some real-world examples of heat energy in action?
Heat energy is crucial in many everyday applications and natural phenomena. Examples include:
- Cooking food: Heat is transferred to alter the food's texture and chemical makeup.
- Weather patterns: The uneven heating of the Earth by the sun creates temperature differences that drive wind and ocean currents.
- Internal combustion engines: The heat from burning fuel is converted into mechanical work to power vehicles.
- Ironing clothes: A hot iron uses conduction to transfer heat, relaxing fabric fibres to remove creases.
6. Why does a substance's temperature stay constant during a phase change, like melting or boiling?
During a phase change, the heat energy added to the substance is not used to increase the kinetic energy of its molecules (which would raise the temperature). Instead, this energy, known as latent heat, is consumed to break the intermolecular bonds holding the substance in its current state (e.g., breaking the solid structure of ice to form liquid water). The temperature only begins to rise again after all the substance has completed the phase transition.
7. What is meant by the term 'latent heat' in physics?
Latent heat is the “hidden” thermal energy that is absorbed or released by a substance during a change of state without any change in its temperature. It is the energy required to alter the phase of a substance. The two main types are the Latent Heat of Fusion (for melting/freezing) and the Latent Heat of Vaporisation (for boiling/condensation).
8. How does the concept of heat relate to the First Law of Thermodynamics?
The First Law of Thermodynamics frames heat as a method of energy transfer. It states that the change in a system's internal energy (ΔU) is equal to the heat (Q) added to the system minus the work (W) done by the system (ΔU = Q - W). This law establishes that heat supplied to a system can either increase its internal energy (making it hotter) or be converted into mechanical work performed by the system.
