Capacitors Flashcards
All versions of energy in capacitor
E = 1/2 QV
E = 1/2 CV^2
E = 1/2 Q^2/C
Energy, Charge, Voltage (normally)
E = QV
charge time current
Q = IT
energy, ITV
E = ItV
Farad meaning
amount of charge stored per unit voltage
Adding capacitance in parallel vs series
Parallel - Normal
Series - Reciprocal
Parallel capacitors distribution and constants
Voltage same
Charge shared and proportional to capacitance
Series capacitors distribution and constants
Charge same
Voltage shared and inversely proportional to capacitance
Discharging (V, Q, I)
V = V0e^-t/RC
Q = Q0e^-t/RC
I = I0e^-t/RC
Time constant meaning
Time taken for charge (&pd ¤t) to drop by 1/e
Or time taken for it to charge to get to (1-1/e)
time constant equation
τ = CR
when time is time constant:
V = V0 e^-1
halving time, time constant
H.t = ln(2) τ
Charging capacitor equation
Vc = Vo (1- (e ^-t/RC))
Vc is voltage across capacitance
Vo is cell voltage
Charging capacitor equation (resistor voltage)
Vr = Vo (e ^-t/RC)
Vr is resistor voltage
Vo is cell voltage
current, charging capacitor
Current goes down as capacitor charges
I = Io e^-t/RC
finding time for capacitance to decrease by a proportion
V/Vo = e^-t/RC
where V/Vo is the ratio of how much it decreased
Capacitance physical things equation
C = (εr εo A)/d
material put in middle of capacitor name
dielectric
increase distance when battery connected energy
energy decrease
increase distance when battery disconnected energy
energy increase
p
x10 ^ -12
n
10 ^ -9
M
10 ^ 6
Electric field equation
E = v/d
Electric field force equation
F = QxV / d
How polar molecules work in dielectric
- negative side aligned facing positive plate
- reducing electric field
- V reduces, Q constant so C increases because of equation
