Points to Remember: Thermal Physics - Key Concepts & Definitions for Science Students

Thermal Physics

Key Points to Remember

Fundamental Concepts

The SI unit of heat energy absorbed or evolved is joule (J)
Heat always flows from a system at higher temperature to a system at lower temperature.
Temperature is defined as the degree of hotness of a body. The SI unit of temperature is kelvin (K).
All the substances will undergo one or more of the following changes when heated:
1. Temperature of the substance rises.
2. The substance may change state from solid to liquid or gas.
3. The substance will expand when heated.
All forms of matter (solid, liquid and gas) undergo expansion on heating.
For a given rise in temperature, a liquid will have more expansion than a solid and a gaseous substance has the highest expansion than the other two.
If a liquid is heated directly without using any container, then the expansion that you observe is termed as real expansion of the liquid.
The expansion of a liquid apparently observed without considering the expansion of the container is called the apparent expansion of liquid.
For a given heat energy, the real expansion is always more than that of apparent expansion.
If the atoms or molecules of a gas do not interact with each other, then the gas is said to be an ideal gas or a perfect gas.
Ideal gas equation, also called as equation of state is \(PV = RT\). Here, R is known as universal gas constant whose value is 8.31 J mol^-1K^-1

Understanding Temperature, Thermal Equilibrium, and Absolute Scale in Thermal Physics

Temperature

Introduction to Temperature

TEMPERATURE

Temperature is defined as the degree of hotness of a body. The temperature is higher for a hotter body than for a colder body. It is also be defined as the property which determines whether a body is in equilibrium or not with the surroundings. (or average kinetic enegy of the molecules). Further, temperature is the property, which determines the direction of flow of heat. It is a scalar quantity. The SI unit of temperature is kelvin (K). There are other commonly used units of temperature such as degree celsius (°C) and degree fahrenheit (°F).

1. Absolute scale (kelvin scale) of temperature

The temperature measured in relation to absolute zero using the kelvin scale is known as absolute temperature. It is also known as the thermodynamic temperature. Each unit of the thermodynamic scale of temperature is defined as the fraction of 1/273.16th part of the thermodynamic temperature of the triple point of water. A temperature difference of 1°C is equal to that of 1K. Zero Kelvin is the absolute scale of tempeture of the body.

The relation between the different types of scale of temperature:

Celsius and Kelvin: \( K = C + 273 \)

Fahrenheit and Kelvin: \( [K] = (F + 460) \times \frac{5}{9} \)

\( 0\,\text{K} = –273\,^\circ\text{C} \)

2. Thermal equilibrium

Two or more physical systems or bodies are said to be in thermal equilibrium if there is no net flow of thermal energy between the systems. Heat energy always flows from one body to the other due to a temperature difference between them. Thus, you can define thermal equilibrium in another way. If two bodies are said to be in thermal equilibrium, then, they will be at the same temperature. What will happen if two bodies at different temperatures are brought in contact with one other? There will be a transfer of heat energy from the hot body to the cold body until a thermal equilibrium is established between them. This is depicted in Figure 3.1.

Figure 3.1 Establishing thermal equilibrium

When a cold body is placed in contact with a hot body, some thermal energy is transferred from the hot body to the cold body. As a result, there is some rise in the temperature of the cold body and decrease in the temperature of the hot body. This process will continue until these two bodies attain the same temperature.

Introduction to Thermal Physics | 10th Science Chapter 3 Explained

Thermal Physics - Introduction

THERMAL PHYSICS

INTRODUCTION

Sun is the primary source of thermal energy for all living organisms. Thermal energy is the cause and temperature is the effect. All living organisms need a particular temperature for their survival. In the kitchen, a container with a steel bottom is placed on the induction stove. Do you know why? All of us have a common man’s understanding of thermal energy and temperature. But, in this chapter, you shall learn about thermal energy and temperature in a scientific manner. We shall also discuss about how thermal energy is transferred and the effects of thermal energy.

Illustrations related to thermal physics, including a thermometer, sun, fire, and ice.

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10th Science : Chapter 3 : Thermal Physics : Thermal Physics | Introduction

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