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Temperature and Heat: Definition, Properties and Difference

If we touch a utensil kept on a burning gas stove, it feels very hot while if we touch a utensil placed in a refrigerator, it feels very cold. But we can’t touch every object to tell whether it's hot or cold enough for the process we want to carry on the object. Thus there is a need for a parameter that can tell whether the object is hot or cold.

Table of Contents:

  • Temperature
  • Properties of Temperature
  • Heat
  • Difference Between Temperature and Heat
  • Practice Questions of Temperature and Heat
  • FAQs of Temperature and Heat

Temperature

Temperature is a relative measure, or indication of hotness or coldness of a body.

The SI unit of temperature is Kelvin(K) while Celcius( oC) is the most commonly used unit of temperature. Temperature is usually measured using a device known as a thermometer. These are of different types which will be discussed as separate topics.

One approach to the definition of temperature is to consider three objects, say blocks A, B and C which are in contact such that they come to thermal equilibrium. By equilibrium we mean that they are no longer transferring any net energy to each other. We would then say that they are at the same temperature, and we would say that temperature is a property of these objects which implies that they will no longer transfer net energy to one another. We could say that A is at the same temperature as C even when they are not in contact with each other. This scenario is called the "zeroth law of thermodynamics".

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Also, temperature is a measure of the average kinetic energy of the particles in an object. When temperature increases, the motion of these particles also increases.

Also, an important point related to temperature is the fact that a collision between a molecule having high kinetic energy with one with low kinetic energy will transfer energy to the molecule of lower kinetic energy.

  • For the two collections of the same type of molecules that are in close contact with each other, the collection which has higher average kinetic energy will transfer energy to the collection which has lower average kinetic energy. We would say that the collection with higher kinetic energy has a higher temperature, and that net energy transfer will be from the higher temperature collection to the lower temperature collection. Therefore, then we define temperature in terms of the average translational kinetic energy of the given molecules.

Properties of Temperature

  • Temperature measures a property of a state of a system irrespective of how it got there and thus it is a state function.
  • Temperature is an absolute quantity and thus frames of reference have no importance while measuring the temperature. No matter where we are located in the universe, the temperature of a sun or planet remains the same for all.
  • The normal temperature of the human body is 310 K or 37°C.
  • The freezing point and boiling point of water is  0°C and 100°C.

Heat

Heat describes the transfer of thermal energy between molecules within a system by the virtue of temperature difference. It is measured in Joules. An object can gain or lose heat, but it cannot have heat. Heat is not a property possessed by an object or system rather it is a measure of change. 

Difference Between Temperature and Heat

Heat and temperature are often used interchangeably. We often use these two terms in our day to day life in terms of weather, objects etc. But do you really know the difference between the heat and temperature? It is really important to know the difference between the heat and temperature. They are somewhat interconnected, but contrary to our belief, they really do not mean the same. Knowing the difference  between both can lead to a clearer and precise understanding of the world around us.Let us know more about them.

S. No. Temperature  Heat
1 Temperature is a measure of the relative degree of hotness or coldness of bodies. Heat is a form of energy.
2 Temperature rises when a body is heated and falls when cooled down. Heat flows from a body at high temperature to a body at relatively colder temperature,
3 The SI unit of temperature is Kelvin. The SI unit of heat is Joules.
4 It is measured using a device called a thermometer. It is measured using a device called calorimeter
5 Since temperature is a property, it does not have any working ability. Being a form of energy, heat has the ability to do work.

Practice Problems of Temperature & Heat

Question.1 The hotness of an object is measured by its _______

Answer. Temperature is used to measure the hotness or coldness of an object.

Question.2  An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Answer. (b)

Since both iron ball and water are at the same temperature, therefore heat will not flow in either direction.

Question.3  Out of temperature and heat, which has the ability to do work?

Answer. Since heat is a form of energy it has some ability to do work while temperature is just a degree of hotness or coldness of a body.

Question.4  What is the driving factor for heat to flow between two objects?

Answer . Temperature difference between two objects is the driving factor for flow of heat between two objects.

FAQs of Temperature and Heat

Question.1 What is the SI unit of temperature?

Answer: kelvin is the SI unit of the  thermodynamic temperature.

Question.2 State the dimensional formula of temperature.

Answer: [M0L0T0K1] is the dimensional formula of temperature.

Question.3 State some commonly used temperature scales. 

Answer: Three scales are commonly used for measuring temperature, Celsius and Fahrenheit scales and Kelvin scale.

Question.4 Energy transfer is from a body with higher kinetic energy molecules to a body at lower kinetic energy. True or False?

Answer: True, net energy will flow from a higher kinetic energy body to a body with lower kinetic energy.

Related Topics to Heat and Temperature in Physics

NCERT Class 11 Physics Chapters

Physical World Units and Measurements

Motion in a Straight Line

Motion in a Plane Laws of Motion Work Energy and Power

Particles and Rotational Motion

Gravitation Mechanical Properties of Solids
Mechanical Properties in Liquids Thermal Properties of Matter Thermodynamics
Kinetic Theory Oscillations Waves
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