Three capacitors having capacitances of 8.4 uF , 8.9 uF , and 4.9 uF are connect

Question

Three capacitors having capacitances of 8.4 uF , 8.9 uF , and 4.9 uF are connected in series across a 33-V potential difference.

A. What is the charge on the 4.9?F capacitor? Q3= _____C

B. What is the total energy stored in all three capacitors? U= ____J

C. The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other, with the positively charged plates connected together. What is the voltage across each capacitor in the parallel combination? V=____

D. What is the total energy now stored in the capacitors? U= ____J

Explanation / Answer

a)

Charge on C3 is

Q3=Q=76 uC

b)

equivalent capacitance

1/Ceq=1/8.9 +1/8.4 +1/4.9

Ceq==2.3 uF

Energy stored

E=(1/2)C3V2=(1/2)*(2.3*10-6)*332

E=1.25*10-3 J

c)

Charge stored in each capacitor before dissconnection

Q=Ceq*V=2.3*33=76 uC

Total Charge

Qt=3*76=228 uC

After connecting in parallel equivalent capacitance

Ceq=8.4+8.9+4.9 =22.2 uF

Voltage acorss each capacitor is

V1=V2=V3=Q/Ceq=228/22.2 =10.27 Volts

d)

Energy stored

E=(1/2)QtV =(1/2)*(228*10-6)*10.27

E=1.17*10-3 J

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