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Atomic Physics

5.1 Properties of conductors in electrostatic equilibrium

3 min readLast Updated on August 7, 2024

Conductors play a crucial role in electromagnetism, especially in electrostatic equilibrium. When charges in a conductor are at rest, the electric field inside becomes zero. This happens as free electrons move to cancel out any internal fields.

Surface charge distribution in conductors is key to understanding their behavior. Charges redistribute on the surface to oppose external fields, creating interesting effects like charge accumulation on sharp edges. This principle is used in lightning rods and Faraday cages.

Electrostatic Equilibrium in Conductors

Conditions for Electrostatic Equilibrium

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  • Electrostatic equilibrium occurs when charges are at rest and there is no net flow of charge within a conductor
  • In electrostatic equilibrium, the electric field inside a conductor is zero at all points
  • If an electric field existed inside a conductor, free charges would move until the field is neutralized
  • Conductors contain free charges (electrons) that can move easily within the material in response to an electric field

Charge Redistribution in Conductors

  • When a conductor is placed in an external electric field, charges redistribute themselves on the surface
  • Positive charges accumulate on the surface facing the negative source, while negative charges accumulate on the surface facing the positive source
  • This redistribution of charges creates an induced electric field inside the conductor that opposes the external field
  • The process of charge redistribution continues until the net electric field inside the conductor becomes zero, reaching electrostatic equilibrium

Surface Charge Distribution

Factors Affecting Surface Charge Distribution

  • Surface charge distribution on a conductor depends on its shape and the presence of external electric fields
  • Charges tend to accumulate more densely on sharp edges or points of a conductor (lightning rods)
  • On a spherical conductor, the surface charge distribution is uniform in the absence of external fields
  • The surface of a conductor in electrostatic equilibrium is an equipotential surface, meaning all points on the surface have the same electric potential

Equipotential Surfaces and Electric Field Lines

  • Equipotential surfaces are surfaces on which all points have the same electric potential
  • Electric field lines are always perpendicular to equipotential surfaces
  • The electric field just outside a conductor's surface is perpendicular to the surface
  • The electric field inside a conductor is zero, so there are no electric field lines within the conductor

Electrostatic Shielding

Faraday Cages and Their Applications

  • A Faraday cage is an enclosure made of a conducting material that shields its interior from external electric fields
  • When an external electric field is applied, charges redistribute on the outer surface of the Faraday cage, canceling the field inside
  • Faraday cages are used to protect sensitive electronic equipment from electromagnetic interference (EMI)
  • They are also used in microwave ovens to prevent the escape of electromagnetic waves while allowing visibility through the mesh

Principles of Electrostatic Shielding

  • Electrostatic shielding works by exploiting the properties of conductors in electrostatic equilibrium
  • A conducting shell (Faraday cage) creates a region inside where the electric field is zero, regardless of the external field
  • Charges on the outer surface of the shell redistribute to cancel the external field inside the shell
  • Electrostatic shielding is effective for static electric fields but not for time-varying magnetic fields
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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
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