Thermal Physics is a branch of Physics that deals with the study of heat, temperature, and the processes through which thermal energy is transferred. The International Baccalaureate (IB) syllabus for Thermal Physics covers a range of topics from the basic concepts of solids, liquids, and gases to more advanced topics such as the kinetic model of an ideal gas and phase changes. This document breaks down these complex ideas into smaller, digestible sections, providing detailed explanations and examples to aid understanding.
Solids:
Liquids:
Gases:
Example:
Consider a block of ice, a glass of water, and a balloon filled with air. The ice has a fixed shape and volume, the water takes the shape of its glass but maintains a constant volume, and the air in the balloon expands to fill the balloon's shape.
Conversion between Celsius and Kelvin: $$ T(K) = T(°C) + 273.15 $$
Tip:
Remember that temperature differences in Kelvin are the same as in Celsius: $$ \Delta T(K) = \Delta T(°C) $$
Example:
If the temperature of a room increases from 20°C to 25°C, the temperature change is: $$ \Delta T = 25°C - 20°C = 5°C $$ In Kelvin, this is: $$ \Delta T = 5K $$
Note:
Temperature is a measure of the average kinetic energy of the particles. Phase changes involve changes in potential energy without changing temperature.
Example:
Calculate the heat energy required to raise the temperature of 2 kg of water from 20°C to 30°C. The specific heat capacity of water is 4200 J/kg·K. $$ Q = mc\Delta T $$ $$ Q = 2 \times 4200 \times (30 - 20) $$ $$ Q = 2 \times 4200 \times 10 $$ $$ Q = 84000 \text{ J} $$
Example:
Calculate the heat energy required to melt 1.5 kg of ice at 0°C. The specific latent heat of fusion for ice is 334,000 J/kg. $$ Q = mL $$ $$ Q = 1.5 \times 334,000 $$ $$ Q = 501,000 \text{ J} $$
Note:
During phase changes, the thermal energy affects the potential energy of the molecules, not their kinetic energy.
Example:
Calculate the volume occupied by 2 moles of an ideal gas at a pressure of 101.3 kPa and a temperature of 300 K. $$ PV = nRT $$ $$ V = \frac{nRT}{P} $$ $$ V = \frac{2 \times 8.31 \times 300}{101.3 \times 10^3} $$ $$ V \approx 0.049 \text{ m}^3 $$
Example:
Calculate the number of moles in 88 grams of CO₂. The molar mass of CO₂ is 44 g/mol. $$ n = \frac{m}{M} $$ $$ n = \frac{88}{44} $$ $$ n = 2 \text{ moles} $$
Conduction:
Convection:
Thermal Radiation:
Example:
A hot meteorite hitting the Moon's surface loses energy through conduction (contact with the Moon's surface) and radiation (infrared photons traveling through the vacuum).
Common Mistake:
A common misconception is that conduction and convection can occur in a vacuum. Only radiation can transfer heat in a vacuum.
Thermal Physics encompasses a wide range of concepts essential for understanding the behavior of matter under various thermal conditions. By breaking down these concepts and providing detailed explanations and examples, this document aims to make the subject more accessible and understandable. Whether it's the basic properties of solids, liquids, and gases, or the more complex ideal gas laws and kinetic models, mastering these topics is crucial for a solid foundation in Physics.