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The Coupling Constant

We are now ready to define our electrical ``coupling constant'' kE. Referring to Eq.(15) we have

\begin{displaymath}\phi \; [V] \; = \; k_E \, {Q \; [C] \over r \; [m]} \end{displaymath}

which we can rearrange to read

\begin{displaymath}k_E \; = \; {\phi \; [V] \; \cdot \; r \; [m] \over Q \; [C]} \end{displaymath}

Thus kE must have dimensions of {electric potential times distance per unit charge}; we can pick units of V-m/C to stick with convention. This still doesn't tell us the value of kE. This must be measured. The result is

 \begin{displaymath}k_E %
\; = \; 8.98755\cdots \times 10^9 \; \hbox{\rm V-m/C}
\end{displaymath} (17.19)



Jess H. Brewer
1999-01-12