A closed copper ring of radius is held in a region where fixed external charges…
PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Conductors, capacitance and boundary-value electrostatics · Electric current and circuits
Electricity, Magnetism and Electromagnetism, Ch Current, current density, conductivity and Ohm's law
Problem
A closed copper ring of radius 4.0cm is held in a region where fixed external charges produce a uniform static electric field of magnitude 500Vm−1 lying in the plane of the ring. There is no cell anywhere in the ring, no chemical or mechanical agency acts on the carriers inside the metal, and no magnetic field changes anywhere. A student claims that the external field pushes the free electrons round and round, so a steady current flows in the ring for ever.
((a)) Calculate the work done by this static field on a charge of +2.0C carried once round the circular path of the ring.
((b)) Once the ring has reached electrostatic equilibrium, state the magnitude of the electric field at a point inside the copper.
((c)) Using your two answers, say in one or two sentences what is wrong with this claim, and what a ring would need in it to carry a steady current.