SACE Stage 2 Physics — Topic 2: Electromagnetism

Hollow Conductors

Charges on a conductor rearrange themselves until the field inside is zero. Explore two consequences: a hollow cavity is perfectly shielded from outside fields, and bending a charged wire focuses its field at the convex tip — even without any redistribution of the charges themselves.

Controls

External field strength

Field direction

Show field lines Show electrons Show + ions Show test probe

|E| at probe — outside

The conductor is a metal shell. Its positive ions (+) are pinned in the crystal lattice, but the electrons (−) are free to drift. The external field pushes electrons along the surface until their own field, added to the external field, gives zero net field inside the conductor. Anything in the cavity is perfectly shielded.

Rotate the field and watch the electrons migrate. The side they leave behind is "positive" only because the fixed + ions are no longer covered.