Capacitors, Batteries

k : dielectric constant Capacitors Create a difference in Potential based upon how much charge is stored V = q/C (V) C : Capacitance C = k εo A /d k : dielectric constant

Energy stored in Capacitor E = ½ C V2 = ½ q2 /c

Batteries Produce change in voltage by chemical reaction. Change in Voltage depends on type of chemical, not how much. There is no electrical energy stored in a battery, only chemical potential energy.

We can use a battery to “charge up” a capacitor. V C -Change in voltage around entire loop must be zero! q=C V

Capacitors in parallel Several capacitors in parallel behave like one larger capacitor: Capacitance increases. CE = C1 + C2 + C3 + ………. 2μF 3μF 10μF

Capacitors in Series Several capacitors in series block the flow of charge: Capacitance decreases. 1/CE = 1/C1 + 1/C2 + 1/C3 + ………. 2μF 3μF 10μF

Example: What is the equivalent capacitance of the entire circuit? C1 =2μF C2 = 4μF C3 = 4μF C4 = 2μF

What is the voltage across C1. What is the voltage across C3 What is the voltage across C1? What is the voltage across C3? What is q3 the voltage on C3? 20V C1 =2μF C2 = 4μF C3 = 4μF C4 = 2μF

What is the voltage across C2? What is the voltage across C4? C1 =2μF C2 = 4μF C3 = 4μF C4 = 2μF