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Capacitance

Learn about capacitors, capacitance equations, dielectrics, and practical examples to understand the storing of electric charge in devices.

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Capacitance

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  1. Capacitance

  2. Capacitor • Device that can store electric charge • Two conducting objects are placed near one another but not touching • Power source charges up the plates, when source is removed, plates keep charge

  3. Symbol for capacitor • Typically, the capacitor consists of two parallel plates • The plates can be rolled to form a cylinder with a paper insulator separating the plates

  4. Equation • Amount of charge (Q) acquired by the plates is proportional to the potential difference between the plates (V) Q= CV • C is the Capacitance and depends on the capacitor itself • Units of C is the Farad (F)

  5. Value of C • Depends on the dimensions of the capacitor C = Єo (A/d) • Єo is constant (8.85 x 10-12) • Larger A (area) means more charge can be held • Larger d (distance between plates) means less attraction between plates so less charge is drawn from battery

  6. Example • What is the capacitance of two parallel plates 20cm x 30cm which are seperated by a 1.0mm air gap? • What is the charge on each plate when connected to a 12V battery? • What is the electric field between the plates?

  7. Dielectric • Insulating sheet between plate • Reduces sparking potential • Can get plates closer without touching so more charge can be stored • Increases capacitance by a factor K which depends on the material of the dielectric C =KЄo (A/d)

  8. Example • A capacitor consisting of two charged plates is separated by a distance d and charged by voltage V. While still connected to the battery, a dielectric is slid between the plates. What will happen to Q? What does this mean?

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