The Partial Derivative of B
The Partial Derivative of the Magnetic Flux Density
On this page we define the symbol:
Briefly, this is simply the negative of the rate of change of the B field with respect to time. The Magnetic Flux Density (B) is defined here.
To define this fully, let's say we have a magnetic flux density B, which is a vector field and a function of (x,y,z,t) (3-spatial variables and time). We write the B field in terms of its x-, y- and z-components:
From the partial derivative page, we know that the partial derivative of B with respect to time is the rate of change of the B field in time (that is, we ignore any spatial variation in the B field and are only concerned with how it changes versus time). And the negative sign in Equation  simply negates each of the components. Hence, we can rewrite Equation  as:
Finally, since the B field is measured in Webers/meter^2 [Wb/m^2] and the derivative means "per second" [1/s], then the units of Equation  are Webers/meter-squared-seconds [Wb/m^2-s]. But we also know from the Faraday's Law Equality Page that this is equivalent to Volts/meter^2 [V/m^2].
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