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Capacitorsprepwalk

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Capacitorsprepwalk

  1. 1. PHYSICS CAPACITORS Short revision series
  2. 2. Capaitors  2 conductors separated by an insulator  Capacitance iss the ability of a conductor to store charge. Measured in Farads F.  C = Q  Q p.d V V Q = CV V = Q/C
  3. 3.  Parrallel plate capacitor with an area A and separated by distance d  C = ε0 εr A d  Capacitors in parrallel  C = C1 + C2  Capacitors in series  1/C = 1/C1 + 1/C2
  4. 4. Eg  A parallel plate capacitor is charged to 200V in a vacuum. It has an area of 100mm2 and separated by 20mm space filled with mesh of εr = 5. What is the capacitance?
  5. 5.  C = ε0 εr A d  = 8.85 x 10-12 x 5 x 100 x 10-3 20 x 10-3 = 2.21 x 10-10 F.
  6. 6. Energy stored in a charged capacitor = average potential difference x charge ½ QV V = Q/C W = ½ QQ/C = ½ Q2/C  Can still be expressed as  ½ CV2 substituting Q = CV
  7. 7. Eg  Consider a circuit with 3 capacitors of 4 μF each in parallel with a potential of 50V across the circuit. What is the capacitance? What is the energy stored?
  8. 8.  C = C1 + C2 + C3  = 12 μF  Energy stored = ½ CV2 = ½ x 12 x 10-6 x 502 = 15 x 10-3 J
  9. 9. Uses of capacitors  Tuning in radio circuits  Prevention of sparking in switches  Charge storage  Smoothening rectified current from dc power supplies  Blocking noise in ac amplifiers.
  10. 10. END

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