"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 ()."
"Permeability of Free Space Magnetic fields (represented by the symbol B) can be created by magnets, as shown in the photo up top. But because of that interdependence we talked about, they can also be made by moving electrical charges. (I'm using the shorthand term "charges" for charged particles, like electrons.) This is described by the Biot-Savart law: You can see the magnetic constant () in there. We also have the value of the electric charge ( q) moving with a certain velocity ( v)."
Three electromagnetic constants—the speed of light (c), the magnetic constant (μ0), and the electric constant (ε0)—are interdependent so that knowing two determines the third. The meter is defined via a fixed speed of light of exactly 299,792,458 meters per second, making c an exact value by definition. The magnetic constant μ0 is measured experimentally and combined with the defined c to calculate ε0. Magnetic fields (B) arise from magnets and from moving electric charges according to the Biot–Savart law, and electric current (coulombs per second) generates magnetic fields used in devices like electromagnets.
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