Daily Physicist

Image courtesy of the Wellcome Collection under the Creative Commons Attribution 4.0 International License.

Today is the birthday of

• Giulio Racah (1909-1965).

Today’s Problem

The adult human body contains about 30 trillion human cells (neglecting bacteria). If a person uses 2500 food calories (kcal) per day, what is the average power output per cell in watts?

Answer

In a previous post we calculated that 2500 food calories per day corresponds to 121 watts, so the average power output per cell is

\[\frac{121\,\mathrm{watts}}{30\times 10^{12}\,\mathrm{cells}}=4.0\times 10^{-12}\,\mathrm{watts/cell}\]

or \(4.0\) picowatts (pW) per cell. Incidentally, this is within the range of cosmic microwave background measurements (0.1 to 5 pW).