Presentation on theme: "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."— Presentation transcript:
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
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
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 Capacitor…C = ЄA/d where Є = a constant, A is the area of the plate, and d = distance between the plates.
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.
Dielectrics (17.8) Dielectrics increase the capacitance by a factor of K. K = dielectric constant = material property C = KЄA/d MtlK Vacuum1.0 Paper3.7 Rubber6.7 Waffle9.3
Energy in a capacitor Caps store energy E = ½ CV 2 (V = Voltage, not velocity…duh)
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.
Capacitors in series and parallel The rules for combining capacitors in a circuit is just the opposite as the resistor rules….. CircuitVoltageChargeCequiv ParallelSameAddsCeq=C1+C2 SeriesAddsSame I/C eq = 1/C1 + 1/C2