ELECTRIC FIELDS IN MATTER — Edward Purcell & David Morin
Physics — E&M · em-waves-energy
Problem
Of all the electromagnetic energy in the universe, by far the largest amount is in the form of waves with wavelengths in the millimeter range. This is the cosmic microwave background radiation discovered by Penzias and Wilson in 1965. It apparently fills all space, including the vast space between galaxies, with an energy density of 4⋅10−14 joule/m3. Calculate the rms electric field strength in this radiation, in volts/m. Roughly how far away from a 1 kilowatt radio transmitter would you find a comparable electromagnetic wave intensity?