What is flux?

• Flux is the amount of “something” (electric field, magnetic field, water, whatever you want) passing through a surface.
• The total flux depends on strength of the field, the size of the surface it passes through, and their orientation.

For this discussion lets keep that something as water :

To measure the flux (i.e. water) passing through a surface, we need to know

• The surface you are considering (shape, size and orientation)
• The source of the flux (strength of the field, and which way it is spitting out flux)

Flux Factors

The source of flux has a huge impact on the total flux. Doubling the source will double the flux passing through a surface.

Total flux also depends on the orientation of the field and the surface. When our surface completely faces the field it captures maximum flux, like a sail facing directly into the wind. As the surface tilts away from the field, the flux decreases as less and less flux crosses the surface.

Eventually, we get zero flux when the source and boundary are parallel — the flux is passing over the boundary, but not crossing through it. It would be like holding a bucket sideways under a running Tap. You wouldn’t capture much water (ignoring splashing) and may get a few funny looks.

Total flux also depends on the size of our surface. In the same field, a bigger bucket will capture more flux than a smaller one. When we figure out our total flux, we need to see how much field is passing through our entire surface.

Assuming the same amount of water is leaving and entering (the rate of water falling is a constant), the net flux would be zero. Think of it as X + (-X) = 0

Total flux = (Field Strength * dS * Orientation) for every dS.

Now, we need to figure out how much orientation actually matters. Like we said before, if the field and the surface are parallel, then there is zero flux.

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