Capacitance
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This text is meant to accompany class discussions. It is not everything there is to know about the basics of torque and the two conditions of equilibrium. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)
 
Questions Click for the questions that go with this reading
Capacitors in Parallel

When capacitors are in configured in parallel, the equivalent capacitance goes up. (The "equivalent" is the value of a single capacitor if it was to replace this section of a circuit. The equivalent is used instead of "total" because "total" implies that capacitors are always directly added -and that is not true for series circuits.) Capacitors in parallel add up according to the formula below.

 

Formula

 

This equation makes sense. The original formula for parallel plate capacitors showed that the capacitance goes up as the plates' area gets larger. In a parallel capacitor arrangement, that's why the equivalent capacitance increases.

The charge that resides on each plate is directly proportional to the area of the plate. A larger plate means more room fro charges to sit. Carrying this a step further, the amount of charge stored in each capacitor is proportional to the capacitance too.

By the definition of parallel components, from the video above, the voltage used up by each capacitor in parallel is the same.

 

 

Example 3
  • Question
  • Solution

What is the total capacitance of the circuit below?

 
Example 4
  • Question
  • Solution

What is the total capacitance of this circuit?

 
Capacitors in Series

Unlike capacitors in parallel, when capacitors are in series their equivalent capacitance goes down. They behave according to the formula below.

 

formula

 

Each capacitor in series will use up a difference amount of voltage. But each capacitor in series will all have the same charge.

 

Example 5
  • Question
  • Solution

What is the circuit's total capacitance?

 
 
Example 6
  • Question
  • Solution

What is the circuit's total capacitance?

 

What is a real capacitor?

 

Only watch the first 2 minutes of the video.

This video is made by Makezine. (One of my favorite magazines.)

This YouTube video can be found at http://youtu.be/ZYH9dGl4gUE

 

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by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)