Figure 16-17 shows how we extend the idea of flux to the electric field. Instead of a pipe carrying a fluid, let’s look at a region of space where there is an electric field \(\vec{E}\). We saw in Section 16-5 that the value of \(\vec{E}\) can vary from point to point, so we consider a small enough region that we can treat \(\vec{E}\) as having essentially the same value over that region. We then imagine a small rectangular area \(A\) that we can orient however we like. By analogy to the flux of water in Figure 16-16, we define the electric flux \(\boldsymbol{\Phi}\) (the upper-case Greek letter phi) through the area \(A\) as follows: