Why Electric Flux \Phi is Defined

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Discussion Overview

The discussion revolves around the definition of electric flux \Phi, specifically the expression \Phi = EAcos\theta. Participants explore the reasoning behind the cosine term and its implications in understanding electric flux in relation to the orientation of the electric field and the surface area.

Discussion Character

  • Conceptual clarification, Technical explanation

Main Points Raised

  • One participant questions the inclusion of cos\theta in the definition of electric flux.
  • Another participant explains that the cosine term arises from the dot product between the electric field E and the differential area dA, indicating the projection of E along the area.
  • A different analogy is provided, comparing electric flux to counting bugs hitting a tilted windscreen, suggesting that the number of bugs (or flux) is maximized at 90º and zero at 0º, which relates to the cosine function.
  • Mathematically, it is noted that the flux can be expressed as E.(Añ), where ñ is the unit vector normal to the surface.

Areas of Agreement / Disagreement

Participants present different explanations and analogies regarding the definition of electric flux, but there is no explicit consensus on the understanding of cos\theta.

Contextual Notes

Some assumptions about the orientation of the electric field and surface area are implied but not explicitly stated. The discussion does not resolve the underlying conceptual questions about the definition.

Who May Find This Useful

Individuals interested in understanding electric flux, particularly in the context of physics education or applications in electromagnetism.

yaik
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Why the electric flux [tex]\Phi[/tex] is defined as EAcos[tex]\theta[/tex]?

I don't understand the part about cos[tex]\theta[/tex]...
 
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Welcome to PF!

Hi yaik! Welcome to PF! :smile:

Imagine you want to know the flux of bugs flying horizontally along a road.

If you count the number that go splat on your windscreen, then you'll collect less (in a given time) if the windscreen is tilted: the number will be greatest at 90º, and zero at 0º: it'll be proportional to cosθ. :smile:

Mathematically, flux of a field E through a surface with area A is E.(Añ), where ñ is the unit vector normal (perpendicular) to the surface. :wink:​
 
thx!
 

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