Capacitors (17.7-17.9)

1
Capacitors (17.7-17.9)

• Capacitors are elements used in circuits to store
  electric charge (and energy) and to block surges
  of electricity, protecting circuits

2
Capacitors what are they?

• Caps typically consists of 2 conducting plates
  placed near each other but not touching.
• Sometimes they are wrapped into a cylinder like a
  burrito or one of those healthy wraps

3
Capacitors

• When placed in a circuit and voltage source,
  charges flow onto the plates.
• Q CV total charge on the capacitor
• C is called the Capacitance and its measured in
  Farads.
• C depends on the geometry of the CapacitorC
  ?A/d where ? a constant , A is the area of
  the plate, and d distance between the plates.

4
Capacitors and Dielectrics

• A dielectric is a material which is placed
  between the plates in a capacitor.
• A dielectric does not allow electric charge to
  jump across the gap as easily as air, so higher
  voltages can be used.
• Dielectrics also increase the Capacitance of the
  capacitor.

5
Dielectrics (17.8)

• Dielectrics increase the capacitance by a factor
  of K.
• K dielectric constant material property
• C K?A/d
• Mtl K
• Vacuum 1.0
• Paper 3.7
• Rubber 6.7
• Waffle 9.3

6
Energy in a capacitor

• Caps store energy
• E ½ CV2 (V Voltage, not velocityduh)

7
Capacitors in circuits (19.5)

• Capacitors are commonly used in circuits to store
  energy and influence how quickly the current
  changes.
• Caps in Parallel have the same voltage and you
  find the total charge Q on each plate using Q
  CV
• Caps in Series have the same charge on them.

8
Capacitors in series and parallel

• The rules for combining capacitors in a circuit
  is just the opposite as the resistor rules..
• Circuit Voltage Charge Cequiv
• Parallel Same Adds CeqC1C2
• Series Adds Same I/Ceq 1/C1 1/C2