Which one of the following is the correct relation between the Kelvin temperature (T) and the Celsius temperature (tc)?
- A.These are two independent temperature scales
- B.T = tc
- C.T = tc − 273.15
- D.T = tc + 273.15
Correct answer
Explanation
The correct answer is D, T = tc + 273.15. A kelvin and a degree Celsius are the same size, but the Kelvin scale starts at absolute zero, which is −273.15 °C.
The kelvin is the SI unit of temperature. Absolute zero, 0 K, is the lowest possible temperature, where the thermal motion of particles is at its minimum. Because the two scales have equal steps, converting is just a shift: add 273.15 to a Celsius reading to get kelvin. So water freezes at 273.15 K and boils at 373.15 K at normal pressure, and normal body temperature of 37 °C is about 310 K. Kelvin readings are never negative and are written without the degree sign.
A is wrong: the scales are linked by a fixed relation, since the Kelvin scale is defined from the same unit size.
B is wrong: equal readings would mean the scales share a zero, but 0 °C is 273.15 K.
C is wrong: subtracting 273.15 converts kelvin to Celsius, not the other way round.
Exam tip: K = °C + 273.15; °F = (9/5)°C + 32; −40 is the same on the Celsius and Fahrenheit scales.
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