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Capacitance

Capacitance. 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. Symbol for capacitor Typically, the capacitor consists of two parallel plates

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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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