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You might have come across the word heat several times in your day to day life. Heat is an energy that gives all of us a sense of warmness it is the degree of hotness or coldness of a body or environment. Sun is a natural source of Heat. All the living beings rely on heat for their existence but excess heat deteriorates them.  In short, energy that is transferred from one body to another as a result of a difference in temperature is called as Heat.


In physics, a measure of the warmth or coldness of an object or substance with reference to some standard value. Heat flows from one point to another based on what's the temperature difference is. There will be no transfer of heat if thermal equilibrium is achieved. 

What is Heat?

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Consider a very hot mug of coffee on the countertop of your kitchen. Suppose you forget to drink it, the coffee will gradually cool down. Let’s look at another instance where you want to drink cold water filled with ice cubes during hot summers, the moment you bring the water outside the freezer the ice cubes starts melting. The energy that is lost by the coffee and the mug is being transferred to the colder surroundings. We refer to this transfer of energy from the coffee and the mug to the surrounding air and countertop as heat. Heat is simply the transfer of energy from a hot object to a colder object.
Heat is the transfer of energy and the transfer of energy always takes place from the region of the higher temperature to the region of the lower temperature. Heat is the energy in flow due to the difference in temperature.

Heat and Temperature

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Heat and temperature appears to be the same as both tells about hotness but differs a lot. Here are mentioned some differences between the two:

Heat   Temperature
 Heat (Q) is energy. Unit = Joules.  Temperature (T) is not energy. Unit =Kelvin, Celsius or Fahrenheit.
 Heat is energy that is transferred from one body to another as the result of a difference in temperature.  Temperature is a measure of hotness or coldness expressed in terms of Celsius and Fahrenheit.
 Heat has the ability to do work.  Temperature can only be used to measure the degree of heat.
 It is measured using calorimeter.  It is measured using thermometer.
 It is the measure of the average kinetic and potential energy of the molecules.  It is the measure of kinetic energy of the molecules.

Heat Capacity

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Heat Capacity is that quantity of heat you need to raise the substance temperature by one degree. If Q is the amount of heat given to a substance to increase its temperature by  $\Delta$ T then the heat capacity C is
Heat Capacity Formula
Here Tf is the final temperature and Ti is the initial temperature. It is expressed in Joule per kelvin (J/K).
Heat transfer is the movement of energy flow from a hot point to a cold point. Often the flow takes place between the system and surroundings which depends on the temperature difference between the two. If the system temperature is higher, then the heat flows from system to surroundings else vice-verse.

The rate of heat transfer is the heat transferred through a substance which is directly proportional to the area of the surface (A) and temperature gradient  ($\Delta$ T) / d along the heat transfer path. It is given by
Rate of Heat Transfer Formula

There are three types of heat transfer :
  1. Conduction
  2. Convection
  3. Radiation.
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Heat Conduction

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Heat conduction or Thermal conduction is the transfer of energy between particles in a solid. The transfer of heat is normally from a high temperature object to a lower temperature object. Heat transfer changes the internal energy of both systems involved according to the Law of Thermodynamics.

Take a long piece of metal rod and keep it in the flame. After some time you could gradually observe that the other end of the metal, will also be hot which tells you how the energy gets transferred from one point to another.

Conduction is the transfer of heat between two bodies that are in direct contact with each other. This type of heat transfer is only seen in solids.

The heat conduction equation is
Heat Conduction Equation
Here Q is the heat transfer,
$\Delta$ T is the temperature change,
$\Delta$ t is time taken,
A is the cross sectional area,
$\Delta$ x is the thickness.
The specific heat tells us more about the heat and temperature change for a given mass. It is the amount of heat required to raise a temperature of a unit mass of a substance by 1 degree Celsius. It is given as
Specific Heat Formulae
Here c is the specific heat capacity,
m is the mass of the substance,
$\Delta$ T is the change in temperature,
It is expressed as Joules per kilogram kelvin (J/kg K).
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Latent heat is the energy released or absorbed by a body. It is the amount of energy absorbed or released by a substance during a change in its physical state that occurs without changing its temperature. 

Example: An ice changing to water or liquid, water changing to ice.

In the example above you could see that there will be no change in temperature simply the heat exchange takes place. The energy released comes from the potential energy stored in the bonds between the particles.

Heat absorbed or released as the result of a phase change is called latent heat. The latent heat is normally expressed as the amount of heat (in units of joules or calories) per unit mass of the substance undergoing a change of state.

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Heat Measurement Units

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Heat is a form of energy and thus is measured in Joules. The Earth is hot and that heat is constantly escaping from the deep Earth to the surface to the atmosphere and ultimately into space, flowing from high temperatures at depth to low temperatures in space.

1)Calorie: It is defined as the amount of heat needed to be transferred to increase the temperature of 1 gram of water by 1°C. It is represented by "Cal."

2)British thermal unit (BTU): It is defined as the amount of heat needed to be transferred to increase the temperature of one pound of water through 1°F. It is represented by “BTU.”

3)Joules: Joules is the SI unit of heat. It is equal to the work done when a force of one Newton is applied for a distance of one meter. It is represented by “J.”