04 Relations
T = tC + 273 (Kelvin and Celsius)
tF = 1.8 tC + 32 (Fahrenheit and Celsius), or tC = (tF − 32)/1.8
The size of one degree: 100 Celsius degrees = 180 Fahrenheit degrees = 100 kelvins, so 1 °C = 1 K = 1.8 °F (for differences).
1Freezing point of pure water (melting point of ice)
tC
- 0
tF
- 32
TK
- 273
2Boiling point of pure water
tC
- 100
tF
- 212
TK
- 373
3Normal human body temperature
tC
- 37
tF
- 98.6
TK
- 310
4Average temperature of Earth's surface
tC
- 15
tF
- 59
TK
- 288
- Problem. (a) Convert 20 °C to kelvin and °F.
- (b) A body has a temperature of 283 K; find °C and °F.
- (c) Normal air temperature in an Egyptian summer is 104 °F; find °C and K.
- (d) At which temperature do the Celsius and Fahrenheit scales have the same reading?
Solution. (a) T = 20 + 273 = 293 K; tF = 1.8 × 20 + 32 = 68 °F. (b) tC = 283 − 273 = 10 °C; tF = 1.8 × 10 + 32 = 50 °F. (c) tC = (104 − 32)/1.8 = 72/1.8 = 40 °C; T = 313 K. (d) t = 1.8t + 32 → −0.8t = 32 → t = −40 (−40 °C = −40 °F).