Download Group Problem 11 - University of St. Thomas

Group Problem #11 Phys 112-1 F12 Page 1 of 4
Group problem #11: Capacitors, work and
energy
Two metal spheres are connected by a conducting wire. Sphere 1 has a radius, R1, a charge Q1, and an
electric field strength at the surface of E1. Similarly Sphere 2 has a radius, R2, a charge, Q2 and an electric
field strength at the surface of E2. In this situation R1 is greater than R2.
What is the ratio of V1 to V2?
What is the ratio of Q1 to Q2?
What is the ratio of E1 to E2?
Group Problem #11 Phys 112-1 F12 Page 2 of 4
For a spherical capacitor of plates of radii 40.0mm and 42.0mm, use Gauss’ Law to find the electric field
between the plates. Assume that the inner plate has a charge of +Q. Use the electric field to find the
potential between the plates.
Group Problem #11 Phys 112-1 F12 Page 3 of 4
Consider a parallel plate capacitor with the same capacitance and same separation as the previous
problem. Calculate an equation for the capacitance for the parallel plate capacitor by first finding the
electric field and then the potential between the plates, as in the previous problem.
Group Problem #11 Phys 112-1 F12 Page 4 of 4
A small capacitor (6.0 μF) is charged by a 12V car battery. (a) How much energy is stored in the
capacitor? (b) How much energy did the battery lose? (c) If all the capacitor’s energy could be used to
lift an 80kg man, how far vertically would he be lifted?