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A temperature conversion question asks the following: "The temperature of a sample of a substance changes from 10°C to 20°C. How many Kelvin degrees does the temperature change?"

The correct answer is 10 K, but my question is, why wouldn't you just convert the difference (10°C) to 283 K?

Thanks in advance.

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closed as off-topic by Zhe, Mithoron, A.K., Jon Custer, Tyberius Nov 6 '18 at 20:48

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    $\begingroup$ Let's put it this way. The temperature of a substance was 10°C; how many K was that? Then it changed to 20°C; how many K is that? Now what is the difference? $\endgroup$ – Ivan Neretin Nov 5 '18 at 22:10
  • $\begingroup$ okay thanks, so you don't subtract first? $\endgroup$ – J. Miller Nov 5 '18 at 22:22
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    $\begingroup$ Degrees K are the same size/value as degrees C. The question is asking about the change not the absolute value. $\endgroup$ – Waylander Nov 5 '18 at 22:26
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The point is, we are measuring $\textbf{change}$ in temperature. Not the temperature itself.

Celsius scale has 100 divisions from 0 °C to 100 °C. Kelvin scale also has 100 divisions from 273 K to 373 K. The length of each scale is same. So 100 divisions of Celsius scale = 100 divisions of Kelvin scale or 1 division in each scale is equal.

So ∆°C = (100 − 0)/100 = 1. And ∆K = (373 − 273)/100 = 1 are their change in temperature per division which is same for both.

So ∆°C = ∆K(change)

And K = °C + 273.

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