PHYS 2064
Chapter 16 Problems

Chapter Objectives
  1. Define the electric potential in terms of the potential energy.
  2. Calculate the electric potential for a system of point charges.
  3. Define the capacitance for a set of conductors.  
  4. Calculate the capacitance for a parallel-plate capacitor.
  5. Calculate the capacitance for a system of capacitors connected in parallel and in series.
  6. Describe the effect of a dielectric placed between the plates of a capacitor.
Conceptual Questions
  1. If the potential difference across a capacitor is doubled, by what factor is the energy stored by the capacitor multiplied?
  2. If the charge on a capacitor is doubled, by how much does the capacitance change?
  3. If the area of the plates in a parallel plate capacitor is doubled, then by how much does the capacitance change?
  4. What is the difference between the electric potential and the potential energy?
Problems
  1. A uniform electric field of magnitude 250 V/m is directed in the positive x direction. A 12 x 10-6 charge moves from the origin to the point (x,y) = (20 cm, 50 cm). (a) What was the change in the potential energy of this charge? (b) Through what potential difference did the charge move?
  2. (a) Calculate the speed of a proton that is accelerated from rest through a potential difference of 120 V. (b) Calculate the speed of an electron that is accelerated through the same potential difference.
  3. An electron in the beam of a typical television picture tybe is accelerated through a potential difference of 20,000 V before it strikes the face of the tube. What is the energy of this electron, in electron volts, and what is its speed when it strikes the screen?
  4. Three charges are situated at corners of a rectangle as in Figure P16.13. How much energy would be expended in moving the 8.0 x 10-6 C charge to infinity?
  5. The plates of a parallel-plate capacitor are separated by 0.100 mm. If the material between the plates is air, what plate area is required to provide a capacitance of 2.0 pF?
  6. Three capacitors, C1 = 5.0 x 10-6 F, C2 = 4.0 x 10-6 F, and C3 = 9.0 x 10-6 F, are connected together. (a) Find the effective capacitance of the group if they are all in parallel. (b) Find the effective capacitance of the group if they are all in series.
  7. A parallel-plate capacitor has 2.0 cm2 plates that are separated by 5.0 mm with air between them. If a 12.0 V battery is connected to this capacitor, how much energy does it store?
Solutions