Science
fromWIRED
3 days agoHow Do Metal Detectors Work?
Metal detectors locate metal by generating changing magnetic fields that induce eddy currents and detect the secondary magnetic fields produced by conductive objects.
This means these three values can't be independent; if you know two of them, you can derive the third. How do physicists deal with this? We define the speed of light as exactly 299,792,458 meters per second. (How do we know it's exact? Because we define a meter as the distance light travels in 1/299,792,458 of a second.) Then we measure the magnetic constant () and use that value along with the speed of light to calculate the electric constant ().