Thermal Energy Notes

Temperature

Temperature measures how hot or cold a body is and reflects the average kinetic energy of its molecules. The SI unit for temperature is Kelvin (K).

Heat Transfer

Heat energy always flows from a warmer to a cooler place when there is a temperature difference.

Methods of Heat Transfer

1. Conduction: Particle-to-particle contact, most effective in solids.
2. Convection: Fluid movement in liquids and gases (e.g., air conditioners, boiling water).
3. Radiation: Transfer via electromagnetic waves (e.g., the sun's energy reaching Earth).

Temperature Scales

There are three main temperature scales:

1. Celsius: Widely used.
2. Fahrenheit: Primarily used in the USA.
3. Kelvin (Absolute Scale): Starts at absolute zero (0 K), the lowest possible temperature where molecular motion ceases.

Temperature Scale Comparison

• Fahrenheit: $32 °F$ to $212 °F$
• Celsius: $0 °C$ to $100 °C$
• Kelvin: $273 K$ to $373 K$

Fixed Points on the Celsius Scale

• Lower Fixed Point: $0 °C$ (freezing point of pure water), corresponds to $32 °F$ and $273 K$
• Upper Fixed Point: $100 °C$ (boiling point of pure water), corresponds to $212 °F$ and $373 K$

Temperature Conversion

• $0 K = -273 °C$
• Celsius to Kelvin: $Celsius + 273$
• Kelvin to Celsius: $Kelvin - 273$
• Absolute Zero: $-273 °C$ or $0 K$ (point of no particle energy)
• $°C$ to $°F$: $(°C \times 1.8) + 32$
• $°F$ to $°C$: $(°F – 32) ÷ 1.8$