THE TESLA AND THE GAUSS

If you have a permanent magnet or electromagnet, you might see its “strength” expressed in terms of webers or maxwells. More often, though, you’ll hear or read about units called teslas (T) or gauss (G). These units are expressions of the concentration, or intensity, of the magnetic field within a certain cross section. The flux density, or number of “flux lines per unit cross-sectional area,” is a more useful expressions for magnetic effects than the overall quantity of magnetism. Flux density is customarily denoted B in equations. A flux density of 1 tesla is equal to 1 weber per meter squared (1 Wb/m²). A flux density of 1 gauss is equal to 1 maxwell per centimeter squared (1 Mx/cm²). It turns out that the gauss is equivalent to exactly 0.0001 tesla. That is, 1 G = 10^-4 T, and 1 T = 10⁴ G. To convert from teslas to gauss (not gausses!), multiply by 104; to convert from gauss to teslas, multiply by 10^-4.
If you are confused by the distinctions between webers and teslas or between maxwells and gauss, think of a light bulb. Suppose that a lamp emits 20 W of visible-light power. If you enclose the bulb completely, then 20 W of visible light strike the interior walls of the chamber, no matter how large or small the chamber. However, this is not a very useful notion of the brightness of the light. You know that a single bulb gives plenty of light for a small walk-in closet but is nowhere near adequate to illuminate a gymnasium. The important consideration is the number of watts per unit area. When we say the bulb gives off a certain number of watts of visible light, it’s like saying a magnet has an overall magnetism of so many webers or maxwells. When we say that the bulb produces a certain number of watts per unit area, it’s analogous to saying that a magnetic field has a flux density of so many teslas or gauss.