Thermal Equilibrium and Temperature Scales - SS1 Physics Lesson Note

Thermal Equilibrium: Thermal equilibrium is a state in which two or more objects or systems are at the same temperature and there is no net transfer of heat between them. When two objects are in thermal equilibrium, they have reached a balance in which the rate of heat transfer between them is equal in both directions. This means that the temperatures of the objects are equal, and there is no further change in temperature when they are in contact.

Temperature Scales: Temperature is a measure of the average kinetic energy of the particles in a substance. There are several temperature scales used to measure and express temperature. The most commonly used temperature scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K).

1. Celsius (°C) Scale: The Celsius scale is based on the concept of dividing the range between the freezing point and boiling point of water into 100 equal intervals. The freezing point of water is defined as 0°C, and the boiling point of water is defined as 100°C at standard atmospheric pressure. This scale is commonly used in everyday life and scientific applications.

2. Fahrenheit (°F) Scale: The Fahrenheit scale is mainly used in the United States and a few other countries. It was developed by Daniel Gabriel Fahrenheit. The scale is based on dividing the range between the freezing point and boiling point of water into 180 equal intervals. The freezing point of water is defined as 32°F, and the boiling point of water is defined as 212°F at standard atmospheric pressure.

3. Kelvin (K) Scale: The Kelvin scale is an absolute temperature scale and is commonly used in scientific and technical applications. It is based on the properties of an ideal gas and the concept of absolute zero, the lowest possible temperature at which all molecular motion ceases. The Kelvin scale does not use the degree symbol. The freezing point of water is 273.15 K, and the boiling point of water is 373.15 K at standard atmospheric pressure.

The relationship between the different temperature scales can be expressed using conversion formulas. For example, the Celsius and Kelvin scales have a simple linear relationship: K = °C + 273.15. Similarly, there is a conversion formula between Celsius and Fahrenheit: °F = (°C × 9/5) + 32.

These temperature scales allow us to quantify and compare the thermal energy of objects and systems and provide a standardised way to express temperature measurements.