CONCEPT OF TEMPERATURE
CONTENTS
1.0 Introduction
2.0 Objectives
3.0 Main Content
3.1 Concept of Temperature and Heat
3.2 Concept of Temperature
3.2.1 Thermal Equilibrium
3.2.2 The Zeroth Law of Temperature
3.3 Scale of Temperature
3.3.1 Specification of Fixed Points
3.3.2 Factors for Changes in Fixed Points
3.3.3 The Temperature Scales
3.4 Specification of Interpolation
3.4.1 Definition of Temperature on Celsius Scale
3.4.2 Definition of Temperature on Fahrenheit Scale
3.5 Thermodynamic Scale
4.0 Conclusion
5.0 Summary
6.0 Tutor - Marked Assignment
7.0 References/Further Readings
1.0 INTRODUCTION
You will recall that the concepts of length, mass and time are regardedas fundamental quantities during the study of elementary mechanics.
You also learn about derived quantities such as force, momentum and energy. In this unit, you will be introduced to another fundamental quantity called temperature.
Temperature is a fundamental quantity in the study of heat (thermal energy) or thermodynamics. Some students usually get confused with the concept of temperature and heat. Heat is a form of energy.
Temperature is a sensation of hotness and coldness. Hence in this unit we shall make an attempt to differentiate between the two. We would then explain the concept of temperature by using the zeroth law of
thermodynamic. Having done this, we would then establish how the temperature of a body is measured through the use of thermometers with emphasis on their thermometric properties. In the next unit, you will learn about the types of thermometers.
2.0 OBJECTIVES
After the end of this unit, you should be able to:
● differentiate between temperature and heat
● define the concept of temperature
● explain the terms used for the zeroth law of thermodynamics
● state the law of thermodynamics
● define temperature scales
● solve problems on conversion of temperatures on Celsius
Fahrenheit and Absolute scales.
3.0 MAIN CONTENT
3.1 Concept of Temperature and Heat
The concepts of temperature and heat are two kinds of concepts in
physics that are so closely related that may confuse you as a learner in the study of physics. You need to be clear in your mind what exactly they mean.
You will remember that in your study of mechanics you learnt various forms of energy. Heat was among them. Heat measurement is usually referred to as Calorimetry. Also in the study of Integrated Science, you will also recall that temperature is the degree of coldness or hotness of a body. Temperature measurement in physics is referred to as
thermometry. Then the question arises: Why Heat a form of energy?
It is a form of energy because we use it to do work for us.
In the history of Industrial Revolution, heat engines were used to perform various kinds of work as in the textiles factories and in the locomotive engines used for transport. Besides, at home we use it for cooking and ironing our clothes.
Heat is an intangible agency that causes increase of hotness of a body.
A body is said to be warmer if it receives heat and colder when it losses heat. You will therefore observe that increase in heat content of a body can be caused by any of the following ways:
● direct application of mechanical work (as in friction between two bodies);
● churning of a liquid;
● contact with a hotter body.
Heat therefore flows from a body whose degree of hotness (temperature) is greater to the body of lower degree of hotness (temperature).
Consequently, it is the heat energy that is transferred and not the temperature. As a rule, when two bodies of different temperatures are placed in contact with each other, by definition, the heat lost by one body is absorbed by the other body provided the two bodies neither lose
nor gain heat from the surrounding. In this case we would describe such heat energy interaction as being conserved in the system.
In this unit, we would discuss in details what is meant by temperature and how it is measured using the appropriate scales. Using the zeroth law of thermodynamics will do this. The concept pf heat and its
measurement will be dealt with later.
SELF ASSESSMENT EXERCISE 1
Distinguish between the concepts of heat and temperature.
3.2 Concept of Temperature
The concept of temperature is one of the fundamental concepts in physics. It is rather difficult to define this physical quantity as compared with, say, the length of a body. A meter is a standard length of a bar of platinum – iridium kept in Paris. We can directly copy this bar and use it to find out how many times an object is as long as this bar at anytime and place. This is not the case with temperature. Temperature is
measured through an indirect method, as you will observe later in our discussion. But the question you may ask now: What is temperature?
How can we measure the temperature of a body?
Qualitatively, temperature of a body is the degree of hotness or coldness of a body. However, this answer does not lead us to the quantitative definition of temperature or its operational definition. This is because the sensations of hotness and coldness are highly subjective. The way
you feel is not the same as any other person. Other adjectives used include cold, cool, tepid, warm, etc. Using our feeling of heat to estimate degree of hotness/coldness (temperature) is very personal and very unreliable since its measurement is personal and not a standard one.
Hence when we say the temperature of a body is cold, hot or lukewarm such descriptions are rather too vague to comprehend quantitatively.
Consequently, an independent scale of temperature measurement is therefore highly essential. We would now discuss how we have evolved the scale of temperature measurement.
3.2.1 Thermal Equilibrium
Two bodies may be at different temperature – one hot and the other
cold. The hot one is said to possess more heat energy than the colder body. In another sense, the temperature of the hot body is higher than the colder body.
However, if the two bodies are now in contact with each other, heat energy flows from the hot body to the cold body until the temperatures of the two bodies are the same. The two bodies are then described as being in thermal equilibrium with each other.
Therefore, a thermal equilibrium exists between two bodies when they are in thermal contact with each other and there is no net flow of heat between them.
It is the temperature of a body that determines the direction of flow of heat from that body to another. It will flow until two temperatures are the same i.e. there is a thermal equilibrium. Once, there is a thermal equilibrium between two bodies, then it means that the two temperatures are the same – no net flow. But now the basic question arising: How do we then define the temperature of a body quantitatively? Let us discuss
this concept.
3.2.2 The Zeroth Law of Temperature
The zeroth law of thermodynamics helps us to quantify the concept of temperature objectively. Quantitative definition of temperature involves terms of operations that must be independent of our sense perceptions of hotness or coldness. That is, temperature has to be measure objectively and not subjectively.
It has been observed that there are some systems in which a measurable property of the system varies with hotness or coldness of the system.
CONTENTS
1.0 Introduction
2.0 Objectives
3.0 Main Content
3.1 Concept of Temperature and Heat
3.2 Concept of Temperature
3.2.1 Thermal Equilibrium
3.2.2 The Zeroth Law of Temperature
3.3 Scale of Temperature
3.3.1 Specification of Fixed Points
3.3.2 Factors for Changes in Fixed Points
3.3.3 The Temperature Scales
3.4 Specification of Interpolation
3.4.1 Definition of Temperature on Celsius Scale
3.4.2 Definition of Temperature on Fahrenheit Scale
3.5 Thermodynamic Scale
4.0 Conclusion
5.0 Summary
6.0 Tutor - Marked Assignment
7.0 References/Further Readings
1.0 INTRODUCTION
You will recall that the concepts of length, mass and time are regardedas fundamental quantities during the study of elementary mechanics.
You also learn about derived quantities such as force, momentum and energy. In this unit, you will be introduced to another fundamental quantity called temperature.
Temperature is a fundamental quantity in the study of heat (thermal energy) or thermodynamics. Some students usually get confused with the concept of temperature and heat. Heat is a form of energy.
Temperature is a sensation of hotness and coldness. Hence in this unit we shall make an attempt to differentiate between the two. We would then explain the concept of temperature by using the zeroth law of
thermodynamic. Having done this, we would then establish how the temperature of a body is measured through the use of thermometers with emphasis on their thermometric properties. In the next unit, you will learn about the types of thermometers.
2.0 OBJECTIVES
After the end of this unit, you should be able to:
● differentiate between temperature and heat
● define the concept of temperature
● explain the terms used for the zeroth law of thermodynamics
● state the law of thermodynamics
● define temperature scales
● solve problems on conversion of temperatures on Celsius
Fahrenheit and Absolute scales.
3.0 MAIN CONTENT
3.1 Concept of Temperature and Heat
The concepts of temperature and heat are two kinds of concepts in
physics that are so closely related that may confuse you as a learner in the study of physics. You need to be clear in your mind what exactly they mean.
You will remember that in your study of mechanics you learnt various forms of energy. Heat was among them. Heat measurement is usually referred to as Calorimetry. Also in the study of Integrated Science, you will also recall that temperature is the degree of coldness or hotness of a body. Temperature measurement in physics is referred to as
thermometry. Then the question arises: Why Heat a form of energy?
It is a form of energy because we use it to do work for us.
In the history of Industrial Revolution, heat engines were used to perform various kinds of work as in the textiles factories and in the locomotive engines used for transport. Besides, at home we use it for cooking and ironing our clothes.
Heat is an intangible agency that causes increase of hotness of a body.
A body is said to be warmer if it receives heat and colder when it losses heat. You will therefore observe that increase in heat content of a body can be caused by any of the following ways:
● direct application of mechanical work (as in friction between two bodies);
● churning of a liquid;
● contact with a hotter body.
Heat therefore flows from a body whose degree of hotness (temperature) is greater to the body of lower degree of hotness (temperature).
Consequently, it is the heat energy that is transferred and not the temperature. As a rule, when two bodies of different temperatures are placed in contact with each other, by definition, the heat lost by one body is absorbed by the other body provided the two bodies neither lose
nor gain heat from the surrounding. In this case we would describe such heat energy interaction as being conserved in the system.
In this unit, we would discuss in details what is meant by temperature and how it is measured using the appropriate scales. Using the zeroth law of thermodynamics will do this. The concept pf heat and its
measurement will be dealt with later.
SELF ASSESSMENT EXERCISE 1
Distinguish between the concepts of heat and temperature.
3.2 Concept of Temperature
The concept of temperature is one of the fundamental concepts in physics. It is rather difficult to define this physical quantity as compared with, say, the length of a body. A meter is a standard length of a bar of platinum – iridium kept in Paris. We can directly copy this bar and use it to find out how many times an object is as long as this bar at anytime and place. This is not the case with temperature. Temperature is
measured through an indirect method, as you will observe later in our discussion. But the question you may ask now: What is temperature?
How can we measure the temperature of a body?
Qualitatively, temperature of a body is the degree of hotness or coldness of a body. However, this answer does not lead us to the quantitative definition of temperature or its operational definition. This is because the sensations of hotness and coldness are highly subjective. The way
you feel is not the same as any other person. Other adjectives used include cold, cool, tepid, warm, etc. Using our feeling of heat to estimate degree of hotness/coldness (temperature) is very personal and very unreliable since its measurement is personal and not a standard one.
Hence when we say the temperature of a body is cold, hot or lukewarm such descriptions are rather too vague to comprehend quantitatively.
Consequently, an independent scale of temperature measurement is therefore highly essential. We would now discuss how we have evolved the scale of temperature measurement.
3.2.1 Thermal Equilibrium
Two bodies may be at different temperature – one hot and the other
cold. The hot one is said to possess more heat energy than the colder body. In another sense, the temperature of the hot body is higher than the colder body.
However, if the two bodies are now in contact with each other, heat energy flows from the hot body to the cold body until the temperatures of the two bodies are the same. The two bodies are then described as being in thermal equilibrium with each other.
Therefore, a thermal equilibrium exists between two bodies when they are in thermal contact with each other and there is no net flow of heat between them.
It is the temperature of a body that determines the direction of flow of heat from that body to another. It will flow until two temperatures are the same i.e. there is a thermal equilibrium. Once, there is a thermal equilibrium between two bodies, then it means that the two temperatures are the same – no net flow. But now the basic question arising: How do we then define the temperature of a body quantitatively? Let us discuss
this concept.
3.2.2 The Zeroth Law of Temperature
The zeroth law of thermodynamics helps us to quantify the concept of temperature objectively. Quantitative definition of temperature involves terms of operations that must be independent of our sense perceptions of hotness or coldness. That is, temperature has to be measure objectively and not subjectively.
It has been observed that there are some systems in which a measurable property of the system varies with hotness or coldness of the system.
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