Practice question · Multiple choice
The displacement field D satisfies Gauss's law using only free charge, whereas the electric field E responds to all charge. What follows from this distinction when determining the actual electrostatic force experienced by a test charge inside a polarised dielectric?
Hints
- Which field is defined directly in terms of the Lorentz force on a charge?
- Do the microscopic dipole charges cease to exert forces simply because we re-expressed Gauss's law?
Show the answer
C. The force depends on E because bound charges exert physical forces
Why
Confusing D with the force-mediating field overlooks that bound charge is physically real. D is merely an auxiliary construct that absorbs polarisation into Gauss's law; test charges experience the net Coulomb force from both free and bound sources combined.
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