Capacitance  :              

Parallel-plate Capacitor :       ;      

If the capacitor is isolated, the presence of the dielectric decreases the potential difference between the plates.

If the capacitor is connected to a battery, the presence of the dielectric increases the charge stored in the capacitor.

The introduction of the dielectric increases the capacitance of the capacitor..

Isolated Sphere  :          C = 4πεr

Capacitors in parallel : C = C₁ + C₂ + C₃    

Capacitors in series  : 

Energy stored in a charged capacitor :

If the capacitor is isolated,     is used.

If the capacitor is connected to a battery,     is used

Charging and discharging of a capacitor in R C circuits

Charging a capacitor: Q = Q_o ( 1 - e^-t/RC ) and  V = V_o ( 1 - e^-t/RC )

Discharging a capacitor :       Q = Q_o e^{- t/RC}  ;              V = V_o e^-t/RC  

 In RC circuit

1.  The p.d. across C decreases or increases exponentially and does not change suddenly.

2.   When steady state is reached, the capacitor has infinite resistance ( equivalent to open circuit ).

Using a Reed Switch :            I = C V f

Analogy between a charged capacitor and a stretched spring

Solutions to Problem Set 1 - 4