How materials respond to an electric field. Conductors and shielding, dielectrics and polarisation, the capacitor, capacitance, the parallel-plate capacitor and the effect of a dielectric slab.
3 lessons, about 2 h5 simulations11 problems9 practice questionsPython in every lesson
Created by StemPy LabIn a conductor at rest the free charges settle until the field inside is zero. So the excess charge sits on the surface, the whole conductor has one potential, and the field just outside is , at right angles to the surface. A hollow conductor shields its cavity. A dielectric has no free charges. In a field it becomes polarised, and the charges on its faces cut the field inside to .
A capacitor is two conductors with equal and opposite charges and . The ratio is its capacitance, in farad, and it depends only on the shape of the conductors and the material between them. For two parallel plates . For a sphere , and for two concentric spheres .
A dielectric that fills the gap multiplies the capacitance by , . With the battery connected the voltage stays and the charge grows by . With the battery removed the charge stays and the voltage and the field fall to . A slab of thickness gives , and a metal slab gives .
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