In this topic we will calculate the capacitance of a system of concentric cylindrical shells. The next figure presents the geometry of this topic. Two conducting and concentric cylindrical shells, infinitely long, constitute a system that some capacitance, C. Begin by noting that we can only determine the capacitance per unit length, C/L, because the […]

# Physics

## Kinetic and Radiative Energy of a Falling Electron

A charged particle that is accelerating emits radiation. Through the study of electrodynamics we often encounter moving charged particles without considering the issues of radiation. For example, the energy of a collection of charges may be calculated in part by solving for the energy involved in bringing those charges together from infinity. Radiation that they […]

## Why Not to Use Aluminum in Your Langmuir Probes

I have made a fair number of Langmuir probes during the time I have been running experiments for my thesis. Some of the plasma facing material is aluminum, which I used because it was easy enough to machine that I could do it myself. The benefit of being able to do this myself is that […]

## Electrostatic Potential with Spherical Boundary Conditions

One of the many mathematical techniques that are useful in the study of electrostatics is called the separation of variables method. This topic covers the application of this method to a situation in which the electrostatic potential in a spherically symmetric system is known. In such a system, the potential (potential and electrostatic potential are […]

## Magnetic Field from a Cylinder’s Magnetization

It is not intuitively obvious how an object’s magnetization relates to the magnetic field it generates. To develop a better physical picture of this phenomena consider an object with a given magnetization and then solve for the resulting magnetic field, B. A cylinder of radius, R, and length, L, in which R << L (i.e. […]

## Frequency Filtering in IDL Using the Butterworth Function

When IDL released version 6.3 they included a function called BUTTERWORTH. This function generates the Butterworth filter function commonly used in frequency filtering of time series data. I have previously used a Butterworth filter by generating my own array. Since it is almost always simpler to use provided functions, I decided to use this new […]