16: CGS Electricity and Magnetism
- Page ID
- 5521
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)An older system of units, still used by some authors, was the CGS (centimeter-gram-second) system. In this system, a dyne is the force that will impart an acceleration of 1 cm s-2to a mass of 1 gram. An erg is the work done when a force of one dyne moves its point of application through 1 cm in the line of action of the force. It will not take the reader a moment to see that a newton is equal to 105 dynes, and a joule is 107 ergs. As far as mechanical units are concerned, neither one system has any particular advantage over the other.
- 16.1: Introduction
- We are accustomed to using MKS (metre-kilogram-second) units including meters, kilograms, and seconds. For electricity and magnetism, we extended the MKS system by adding an additional unit, the ampère, to form the MKSA system. This in turn is a subset of SI (le Système International des Unités), which also includes the kelvin, the candela and the mole.
- 16.2: The CGS Electrostatic System
- This page defines the CGS electrostatic unit (esu) of charge, the statcoulomb, and its implications for potential difference and capacitance. It describes that one statvolt is the work for moving one esu of charge, with conversion techniques to SI units outlined. Various capacitance relations and formulas for potential fields and dipole moments are included.
- 16.3: The CGS Electromagnetic System
- One CGS emu of magnetic pole strength is that pole which, if placed 1 cm from a similar pole in vacuo, will repel it with a force of 1 dyne. The system is based on the proposition that there exists a "pole" at each end of a magnet, and that point poles repel each other according to an inverse square law.
- 16.4: The Gaussian Mixed System
- A problem arises if we are dealing with a situation in which there are both “electrostatic” and “electromagnetic” quantities. The “mixed system”, which is used very frequently, in CGS literature, uses esu for quantities that are held to be “electrostatic” and emu for quantities that are held to be “electromagnetic”, and it seems to be up to each author to decide which quantities are to be regarded as “electrostatic” and which are “electromagnetic.
- 16.5: Conversion Factors
- This page explains the challenges of interpreting equations in different unit systems, focusing on CGS and SI. It discusses the confusion from varying units and conversion factors, providing a list of essential conversions between these systems. The text emphasizes the coherence of the SI system compared to CGS, which requires constant conversions, and suggests improving dimensional analysis for better understanding.
- 16.6: Dimensions
- This page emphasizes the significance of dimensional analysis in validating equations in electromagnetic phenomena, particularly in identifying missing terms like permittivity and permeability. It presents examples, such as the equivalent width of spectrum lines and power from an accelerating charge, to demonstrate correcting equations by adding constants.