Capacitors, Batteries
Capacitors
• Create a difference in Potential based upon how much charge is stored
V = q/C (V) C : Capacitance
C = k εo A /dk : 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?
20V
C1 =2μF
C2 = 4μF
C3 = 4μF
C4 = 2μF
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?
20V
C1 =2μF
C2 = 4μF
C3 = 4μF
C4 = 2μF