EMC Question of the Week: July 16, 2018
Gauss’ Law, ∇∙D = ρ, basically tells us that lines of electric flux
- have no beginning or end
- start and stop on electric charge
- are stronger in permeable materials
- are stronger in liquids
Answer
The correct answer is "b." In this equation, D is the electric flux density (a vector field) and ρ is electric charge density (a scalar field). The divergence of a vector field is a measurement of how much the field strengthens or weakens at a given point. Lines of electric flux are only strengthened or weakened by electric charge.
In regions with no electric charge, electric flux lines can neither start nor stop. At the interface between free space and a dielectric with no free charge, the magnitude of an electric flux line doesn't change; however the magnetic of the corresponding electric field line will change. It will be weaker in the dielectric, because D = εE. There is no inherent relationship between the permeability or density of a material and the electric flux strength.
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