Introducing capacitance is one area where simulations can be a valuable supplement to classroom demonstrations. We have several excellent capacitor demonstrations in our collection, but using them in conjunction with a simulation lets students see the invisible details of the behaviour of electric fields and currents.


  • oPhysics Capacitor Lab by Tom Walsh illustrates the basic principles of a parallel plate capacitor. The voltage across the capacitor is shown and you can independently vary the input voltage, plate size and spacing, and resistance of the circuit. When using, note that after changing parameters you will need to close the switch to turn the current on again.


  • PhET Capacitor Lab is similarly a model of a parallel plate capacitor, but offers different features. The power to the capacitor circuit is turned on and adjusted by a slider on the battery image; the current is also reversible here, useful for illustrating what is and is not polarity dependent. Meters can display voltage, capacitance, charge, and stored energy. Additional tabs take you to variations of the model. In one, you can add a dielectric material and vary its dielectric constant, or select from a few popular materials; in the other, you can add multiple capacitors in series and parallel, each with independently adjustable capacitance.


  • Capacitor Interactive Tutorial by MagLab, the National High Magnetic Field Laboratory shows the function of a capacitor in a simple motor circuit, similar to one of our popular demonstrations - but now students can see the electrons in action.