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Review Problems on Static Fields

• What is the ratio of the electric to gravitional force on two electrons 1 nanometer apart?
• Is there a point of stable equilibrium for a positive charge in the interior of an isosolese triangle with negative charges at the vertices?
• Be sure you can do the Gauss' law examples in sections 5-5 to 5-9.
• Near the earth's surface the potential gradient is about 100 V/m.  Uses Gauss' law to deduce the surface charge density.  Incidentally, the potential difference between the surface and the earth's outer conducting layer is about 400,000 V.
• Show that Gauss' law implies Coulombs' law.
• Show that the fact that the field inside a conductor is zero implies the inverse square law.
• How long would it take an electron to travel down 1 meter of 1 mm diameter copper wire?  Assume that there are 10 E 29 free electrons per cubit meter.
• Compute the magnetic field of a long wire using Ampere's law.
• Now compute the field of two wires, with currents in the same and in opposite directions.
• Compute the magnetic field of a long solenoid of N turns.
• Be sure you understand the factor of 1/2 in front of Equation 8.28.  Then verify 8.30.