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For more information, please see full course syllabus of AP Physics C/Electricity and Magnetism
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Lecture Comments (1)

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Post by Suhaib Hasan on October 28, 2012

What is the exact reason that a positive charge has a higher potential than it's negative counterpart? Is it because the positive part is acts as a source?

Calculating Capacitance

  • Isolated conducting sphere: may be taken as a capacitor if we imagine that there is a spherical conducting shell at infinity. In this case, C = 4*pi*epsilon_0*R, where R is the radius of the sphere.
  • Spherical capacitor: composed of a conducting sphere of radius a surrounded by a spherical conducting shell of radius b. To find C, we put +Q on the sphere, -Q on the shell, and calculate the potential difference V. Then C = Q / V. We find that the capacitance is given by C = 4*pi*epsilon_0*a*b / (b – a).
  • Parallel-plate capacitor: C = epsilon_0 * A / d, where A is the plate area and d is the separation between the plates.
  • Cylindrical capacitor: A conducting cylinder of radius a surrounded by a coaxial cylindrical sheel of radius b. The capacitance per unit length is

    C / L = 2*pi*epsilon_0 / ln(b / a)

Calculating Capacitance

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Considering a Sphere 0:28
    • Placing Charge on Sphere
    • On the Surface of Sphere
  • Spherical Capacitor 9:20
    • Sphere of Radius a and Shell of Radius b
    • Positive Charge on Outer Sphere
    • Negative Charge on Inner Sphere
    • Calculating Potential Difference
  • Parallel Plate Capacitor 22:38
    • Two Plates with Charges Positive and Negative
    • Separation of Plate
  • Cylindrical Capacitor 28:40
    • Inner Cylinder and Outer Cylindrical Shell
    • Linear Charge Density
  • Example 1: Parallel Plate Capacitor
  • Example 2: Spherical Capacitor