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Method of images
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Solve problems with conductors by adding fictitious charges.
A charge near a grounded conducting plane produces the same field as if there were an opposite image charge behind the plane. It makes boundary problems solvable.
A +q at distance d from a plane is attracted with F = kq²/(2d)².
Valid only outside the conductor.
In more detail
The method of images replaces a conductor with imaginary charges placed so the boundary conditions are satisfied. It solves problems such as a point charge near a grounded plane.
Real-world uses
- Engineers use image charges to model conductors near charges.
- Physics teaching uses images to solve symmetric problems.
- Physicists solve charge problems near a grounded metal plane by imagining a mirror charge on the other side.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Are image charges real?
No, they are a mathematical device valid only in the region of interest.
Why does it work?
Because the solution must satisfy the boundary condition on the conductor, and images can enforce it.
Is the image charge real?
No. It is a mathematical device that gives the correct field in the region of interest, not a physical charge.
Related topics in Electrostatics
Millikan oil drop experiment · Motion of charge in uniform field · Cathode ray tube · Poisson's and Laplace's equations · Multipole expansion · Boundary conditions at interfaces