What is Absolute temperature? — Physics

Definition 2.6 High School Physics · Chapter 2 — Light Spectra and the Message of Light

For radiation laws, the absolute temperature is counted not from the freezing point of water but from the coldest state possible, $-273{}^{\circ}\mathrm{C}$ . The unit is the kelvin (symbol $\mathrm{K}$ ), with the same size of degree:

T \text{ (in } \mathrm{K}) = \theta \text{ (in } {}^{\circ}\mathrm{C}) + 273 .

Thus a room at $20{}^{\circ}\mathrm{C}$ is at $293\,\mathrm{K}$ , and the surface of the Sun, near $5500{}^{\circ}\mathrm{C}$ , is near $5800\,\mathrm{K}$ .

The visible band of a continuous spectrum at three temperatures: the cooler the source, the dimmer the band — and the blue end fades first.

Examples

Example 2.9 (Taking the Sun’s temperature)

The Sun’s continuous spectrum is most intense near $\lambda_{\max} = 500\,\mathrm{nm}$ . Wien’s law gives its surface temperature:

T = \frac{2.90 \times 10^{-3}\,\mathrm{m}\,\mathrm{K}}{5.00 \times 10^{-7}\,\mathrm{m}} = 5800\,\mathrm{K},

about $5500{}^{\circ}\mathrm{C}$ — measured from $150$ million kilometers away, with a prism and a division.

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Examples

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