Field Lines

• Since Coulomb’s Law is an inverse square law, we can use the density of field lines to represent the magnitude of the field !!

  • Consider the electric field produced by a single point charge:
  • The field is spherically symmetric.
    • ie magnitude of E-field depends only on R
    • at radius R, magnitude of E-field = E = kQ/R2
    • suppose N field lines at surface of sphere of radius R

Note: the density of field lines is proportional to the magnitude of the field as promised only because E is inversely proportional to R2!!

Then, the density of field lines on the surface of sphere is given by:

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