A story currently doing the rounds by email provides detailed instructions for cooking an egg by placing it between two cell phones. Here is my attempt to check its validity.
One egg weighs about 50 g, and we can assume that to make it boil we want to warm it from 20 °C to 100 °C. For heating it we would need about 4 J / g / °C, and therefore 80 * 50 * 4 = 16 kJ (this is without taking into account the increasing thermal losses as the egg's temperature rises.) The web page claims that one can bring the egg to boil in 3 minutes, i.e. 180s. Therefore, the egg must be powered at 16 kJ / 180 s = 88W. To get this figure into perspective we calculate the equivalent power / kg, which is 88 W / 50 g = 1760 W / kg. The specific absorption rate (SAR) for mobile phones in Europe is 2 W / kg; three orders of magnitude less than the required power.
Interestingly, comments in a Slashdot article arrived to similar conclusions using arguments such as the above (with different fudge factors), an analogy with microwave ovens, and by working from the phone's battery capacity. Back of the envelope calculations are surprisingly robust.Read and post comments, or share through
Last modified: Tuesday, February 7, 2006 3:54 pm
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