Overview
This lecture explains the differences between Celsius, Kelvin, and Fahrenheit temperature units and provides methods for converting between them.
Celsius and Kelvin
- Celsius (°C) is commonly used in science; water freezes at 0°C and boils at 100°C.
- Kelvin (K) is the SI unit for temperature; water freezes at 273.15 K and boils at 373.15 K.
- 0 K (absolute zero) is the lowest possible temperature; no degree symbol is used for Kelvin.
- Celsius and Kelvin scales have equal intervals (1°C = 1 K).
- To convert from Celsius to Kelvin: K = °C + 273 (typically omitting the .15 in calculations).
- To convert from Kelvin to Celsius: °C = K - 273.
Fahrenheit
- In Fahrenheit (°F), water freezes at 32°F and boils at 212°F (180° interval).
- Fahrenheit degree intervals are different from those in Celsius and Kelvin.
- To convert Celsius to Fahrenheit: °F = (9/5 × °C) + 32.
- To convert Fahrenheit to Celsius: °C = (5/9 × (°F - 32)).
Example Conversions
- 25°C = 25 + 273 = 298 K; 127°C = 127 + 273 = 400 K.
- 25°C = (9/5 × 25) + 32 = 77°F.
- 100°C = 212°F (boiling point of water); -20°C = -4°F.
- 36°F = (5/9 × (36 - 32)) ≈ 2.22°C.
- 0°F = (5/9 × (0 - 32)) ≈ -17.78°C.
Special Temperature Relationship
- -40°C equals -40°F; only temperature where Celsius and Fahrenheit values are numerically equal.
Conversion Recommendations
- Convert Fahrenheit to Kelvin (or reverse) by first converting to Celsius, then to the desired unit.
Key Terms & Definitions
- Celsius (°C) — Metric temperature unit; 0°C is freezing and 100°C is boiling point of water.
- Kelvin (K) — SI unit for temperature; starts at absolute zero (0 K).
- Fahrenheit (°F) — Temperature unit mainly used in the US; water freezes at 32°F and boils at 212°F.
- Absolute Zero — Lowest possible temperature, 0 K or -273.15°C.
Action Items / Next Steps
- Practice temperature conversions between Celsius, Kelvin, and Fahrenheit using the given formulas.