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The SI unit of heat is Joules (J) which is the same as the unit of energy as heat is the form of energy. Heat is the amount of energy that is transferred from one body to another. Heat flows from the body with a higher temperature to the one with a lower temperature.
- The transfer of energy usually occurs in three different ways like conduction, convection, and radiation.
- The heat formula is given as Q = mcΔT.
- Heat is a form of thermal energy.
- Heat transfer usually takes place until two or more bodies attain equilibrium.
- Some of the other units of heat are BTU and Calorie, apart from Joules (J).
Key Terms: Unit of Heat, Heat Transfer, Heat Energy, Joules, Temperature, Energy, Heat, Calorie, Molecules, Heat units
What is Heat?
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Heat can be defined as the flow of energy passing from a warmer to a cooler body. Thus, with an increase in the temperature of a body, the vibration of molecules or atoms increases. Further, these vibrations are transmitted from one part of the body to another. The measure of energy with which these molecules are seen to vibrate in a system is often referred to as the heat stored in that object.
Heat Transfer
The direction of flow of heat energy typically occurs from the substance of higher temperature to lower temperature. The reason why this happens is due to the molecules vibrate faster, further transferring energy to the molecules which are vibrating slower. The vibrational energy is also called Heat Content. The heat content in the body is responsible to make the object hot or cold. The greater the heat content, the hotter the object will be.
Also Check: Hess’s Law of Constant Heat Summation
SI Unit of Heat
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The SI unit of Heat is Joules. The amount of energy that is required to raise the temperature of a given body (mass) by a unit ie. by one degree is called Joules.
- 4.184 Joules of energy (heat) are required to raise the temperature of a unit weight of water by a unit degree.
- The transfer of energy from a body with a higher temperature to a body with a lower temperature is defined as Heat.
Note: Calorie is frequently used as a unit for heat energy. However, it is not a SI unit of heat. One calorie can be expressed as the amount of energy which is needed to raise the temperature of an object by 1 degree Celsius.
Frequently Asked QuestionsWhat is temperature? Temperature helps in the measurement of the hotness or coldness of an object. Name the various SI units of heat. Joules, Calories and BTU are some of the SI units of heat. Name the SI unit of temperature. The SI unit of temperature is Kelvin. |
Read More: Thermal Conductivity
Other Units of Heat
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Heat is expressed in the terms of calories in the CGS system of units. This is the amount of heat required to raise the temperature of a unit of water by a unit degree celsius.
| 1 kcal = 1000 calories |
Heat can be expressed in various other heat units such as:
- Calorie: Amount of energy required to raise the temperature of 1 gm of clean water by 1o Celsius. Thus,1 Calorie = 4184 Joules.
- Joules: It is the SI unit of Heat energy. Thus, 1 Joule of energy = 0.000239006 kcal or 1 J = 0.000947817 BTU.
- BTU: British Thermal Unit is the amount of energy that is required to raise the temperature of a pound of water by 1o Fahrenheit at sea level. Thus, 1 BTU = 1055.06 J.
| Units of Heat | ||
|---|---|---|
| Units | Symbol | Measurement |
| Calorie | 1 cal | 4.184 J |
| Joules | 1 J | 0.000239006 kcal / 0.000947817Btu |
| BTU | 1 Btu | 1055.06 J |
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What is Heat Energy?
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Heat is a form of energy. The transfer of energy between the systems or the bodies or objects having different temperatures is defined as Heat Energy. The flow of heat is generally from a system having higher temperatures to a system with lower temperatures. Heat energy can also be referred to as Thermal Energy.
Heat is denoted by the symbol Q and can be measured by using the formula:
| \(c =\frac{Q}{m x \Delta T}\) |
- c is the specific heat
- m is the mass of the body
- T is the difference in the temperature
Difference Between Heat and Temperature
There are several differences between Heat and Temperature. Some of them include:
| Heat | Temperature |
|---|---|
| Heat can be expressed as the total energy of a body with molecular motion inside it. | Temperature can be expressed as the measurement of the thermal energy of an object |
| The SI unit of heat is Joules. | The SI unit of temperature is Kelvin. |
| It is represented by Q. | It is represented by T |
Read More: Wien’s Displacement Law
Methods of Heat Energy Transfer
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Heat can be transferred from one body to another body in three ways:
Conduction
When the two systems are in contact with each other directly, the transfer of the heat is known as Conduction.
- The transfer of heat is dependent on the conductivity of the conductor.
- The particles of the system will gain more energy when the substance is heated and the particles will vibrate more hence, conduction will take place.
- Due to this, the particles will collide with the nearby particles and hence the heat will be transferred.
Convection
The transfer of energy from a system with a higher temperature to a system having a lower temperature is termed Convection. It occurs when the warmer areas of either liquid or gas rise to the areas with cooler temperatures in the liquid or gas.
Radiation
In this method of heat transfer, there is no contact between the two systems in which there is a transfer of heat. It can be transferred by thermal radiation. In this method of heat energy transfer, there is no requirement for a medium and no mass is exchanged in the process.
Methods of Transfer of Heat Energy
The video below explains this:
Heat Transfer Formula Detailed Video Explanation:
Read More: Newton’s Law of Cooling
Previous Year Questions
- Heat is flowing through two cylindrical rods … [NEET 1995]
- The two ends of a metal rod are maintained at temperatures … [NEET 2015]
- A sphere, a cube and a thin circular plate all of same … [KCET 2020]
- A certain amount of heat energy is supplied … [KCET 2020]
- The coefficient of thermal conductivity … [KCET 2008]
- The unit of Stefan's constant is … [KCET 2006]
- Two slabs are of the thicknesses … [KCET 2010]
- Two taps supply water to a container … [KEAM]
- If the heat of 110J is added to a gaseous system … [JKCET 2019]
- For an exothermic reaction, the value of … [BHU UET 2004]
- The ratio of the coefficient of thermal conductivity … [BCECE 2007]
Things to Remember
- Heat is the transfer of energy in two systems having different temperatures.
- The SI unit of Heat is Joules.
- Heat can be measured by the formula: \(c =\frac{Q}{m x \Delta T}\).
- Some other heat units are calories and BTU.
- Heat Energy flows from higher temperatures to cooler temperatures.
- Conduction, Convection, and Radiation are the 3 methods through which heat energy can be transferred from one system to another.
Read More:
Sample Questions
Ques. List the uses of Heat Energy. (3 marks)
Ans: The uses are listed below:
- Heat can be used to generate electricity at thermal power plants.
- It can be used for cooking.
- In smoking, heat energy is used.
- For drying, cooling, heating, manufacturing, and baking, heat energy is present.
Ques. What will be the energy required to raise the temperature of the water from 10oC to 70oC? (3 marks)
Ans: As, \(c =\frac{Q}{m x \Delta T}\)
Q = C x m x T
Putting the values in this equation, we will get
Q = (0.7) x (4200) x (70 – 10) = 176.4 kJ
Ques. The temperature of the water of an electric kettle is raised from 20o C to 90oC. The amount of water in the kettle is 1.5 kg. The specific heat capacity of water is given as 4180 J kg-1 K-1. Calculate the energy required for raising the temperature. (5 marks)
Ans: Heat energy can be calculated by using the formula:
Q= C x m x T …….. (i)
We have,
c = 4180 J kg-1 K-1
T1 = 20o C = 20 + 273 = 293 K
T2 = 90o C = 90 + 273 = 363 K
ΔT= T2 - T1
⇒ ΔT= 363 K - 293 K= 70 K
m = 1.5 kg
Putting all the values in equation (i), we will get
Q = (4180 J kg-1 K-1) x (1.5 kg) x (70 K)
⇒ Q = 438 KJ
Ques. Explain the difference between Heat, Temperature, and Internal Energy. (3 marks)
Ans: Heat: Spontaneously transfer of energy from one body to another body due to the difference in the temperatures of the two bodies.
- Temperature: The average kinetic energy of molecules or the atoms of the system is known as Temperature.
- Internal Energy: The energy contained within the system is termed Internal Energy of the system.
Ques. Give the examples of Heat Energy. (3 marks)
Ans: The examples of Heat Energy are as follows -
- Geothermal Energy
- Solar Energy
- Fuel Cell Energy
- Heat Energy from oceans
- Melting of Ice
Ques. What are the various forms of energy? (4 marks)
Ans: The different forms of energy are as follows -
- Heat Energy
- Light Energy
- Mechanical Energy
- Electrical Energy
- Sound Energy
- Nuclear or Atomic Energy
- Gravitational Energy
- Chemical Energy, etc.
Ques. What is Joule? (1 mark)
Ans. One Joule can be expressed as the amount of energy which is exerted or the amount work done when force of one newton has been applied over a meter distance.
Ques. What is Heat Capacity? (2 marks)
Ans. The heat capacity of a substance can be expressed as the amount of heat needed to change the temperature by a degree. The SI units of Heat capacity are Joule or Kelvin (J/K).
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