In this simulation, you can investigate the electric field created by a parallel-plate capacitor, which is a pair of flat metal plates facing one another, one plate positively charged and one plate negatively charged. In the simulation each plate is a square 2 m on each side, and the view is of a two-dimensional slice through the center of the plates.

Here are some things to consider.
1. In this simulation, as long as there is a potential difference one plate is positively charged and the other is negatively charged. When the potential difference is positive, which plate is positively charged, the top plate or the bottom plate? You should be able to use what you know about electric field to answer this. What happens when the potential difference is negative?
2. A parallel-plate capacitor is often used when a uniform electric field is required. How uniform is the field inside the capacitor? Does the uniformity of the field depend on how far apart the plates are?
3. How does the magnitude of the electric field inside the capacitor depend on the potential difference?
4. What determines the shape of the electric field?
5. For a parallel-plate capacitor with infinitely large plates, the uniform electric field between the plates has a magnitude of E = V/d, where V is the potential difference and d is the distance between the plates. How well does that equation work in this situation? Compare results for the two different separation distances available in the simulation.