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A series of free Online High School Physics Video Lessons.

In this lesson, we will learn

  • how to define and calculate power
  • how capacitors store energy
  • how capacitors in series affect current flow
  • how capacitors in parallel affect current flow
  • capacitor circuits
  • RC circuits


Power is the rate of energy use of electric circuit. The way that we calculate power is through the equation
power = current × potential difference = (potential difference)2/resistance = current2 × resistance.
Understanding power.
Define Power.
Calculate the power of a system.


Capacitors store charge and energy. Parallel plate capacitors generally composed of two oppositely charged plates separated by a distance. The equation that we use to determine capacitance is capacitance = stored charge / potential difference. The capacitance of a parallel plate capacitor is proportional to the area of the plates and inversely proportional to the distance between the plates. The unit for capacitance is the Farad.
How capacitors store energy.
Solve basic problems involving parallel plate capacitors.
Find the capacitance of a parallel plate capacitor.

Capacitors in Series

Like currents in series, charge is the same when capacitors are connected in series but the potential difference adds. Unlike currents in series, effective capacitance is found by (1/effective capacitance) = (1/capacitance1) + (1/capacitance2). Effective capacitance is smaller than that of any of the individual capacitors.
How capacitors in series affect current flow.
Derivation and explanation of Capacitors in Series

Capacitors in Parallel

Capacitors in parallel allow the charge a choice of capacitors. Potential difference is the same with multiple parallel capacitors but the charge adds. Like resistance in series, adding capacitors in parallel increases effective capacitance. The formula for determining effective capacitance is effective capacitance = capacitance1 + capacitance2.
How capacitors in parallel affect current flow.
Derivation and explanation of Capacitors in Parallel

Capacitor Circuits

Capacitor circuits are circuits which flow until the capacitors are full. Once the capacitors are full, it is called steady state
How to predict the behavior of capacitor circuits.
Here is an example of a pure capacitor circuit, with a couple parallel sets, and we find the charges stored on each capacitor.

RC Circuits

RC circuits contain resistors and capacitors. Immediately after a switch is closed, completing the circuit, the capacitors behave like wires because they have a potential difference of zero. After the current has been flowing for a long time the capacitors fill and the circuit reaches steady state. In steady state, the resistors in series with the capacitors behave like wires
Combining capacitors and resistors in electric circuits.
An interesting problem involving capacitors, resistance and switches is explained and solved here using charge conservation and the rules for capacitors.

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.
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