Conductors in equilibrium
In a conductor at rest the electric field inside is zero and extra charge sits on the surface.
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Analogy
A metal car body protects you in lightning.
Example
Inside E = 0Charge on outer surfaceField at surface is perpendicular
In practice
Charge on a metal sphere spreads over its outside, so the inside field is zero.
Practice
Flashcards
- What is the field inside a conductor in equilibrium?Zero.
Questions people ask
Why is the field zero inside a conductor?
Free charges inside a metal move until they cancel any field. If a field remained, it would keep pushing charges and the conductor would not be at rest. The charges settle on the surface in a pattern that makes the inside field exactly zero.
How does a Faraday cage work?
A metal cage lets charges rearrange on its surface so the field inside cancels. External electric fields, including radio waves, cannot penetrate. This is why you can lose signal in a lift and why a car protects its occupants during a lightning strike.