# Capacitors

Ok so really confused as to how i find things like mean power and mean current ?
These are two examples of questions i am stuck on:

1) In experiments to pass a very high current through a gas, a bank of capacitors of total capacitance 50 microF is charged to 30 kV. If the bank of capacitors could be discharged completely in 5.0ms what would be the mean power delivered?
A 9.0 MW
B 4.5 MW
C 110 kW
D 22 kW

2) A camera flashgun uses the discharge of a capacitor to provide the energy to produce a single flash. In a particular flashgun a 4700 microF capacitor is initially charge from a 90V supply.

I calculated the charges stored as 0.423 C and the energy stored as 19J but i am stuck on the next part which is:
iii) the average current which flows if total discharge of the capacitor takes place effectively in 30ms
Original post by rosierm
Ok so really confused as to how i find things like mean power and mean current ?
These are two examples of questions i am stuck on:

1) In experiments to pass a very high current through a gas, a bank of capacitors of total capacitance 50 microF is charged to 30 kV. If the bank of capacitors could be discharged completely in 5.0ms what would be the mean power delivered?
A 9.0 MW
B 4.5 MW
C 110 kW
D 22 kW

2) A camera flashgun uses the discharge of a capacitor to provide the energy to produce a single flash. In a particular flashgun a 4700 microF capacitor is initially charge from a 90V supply.

I calculated the charges stored as 0.423 C and the energy stored as 19J but i am stuck on the next part which is:
iii) the average current which flows if total discharge of the capacitor takes place effectively in 30ms

Use E=Pt for the first question to find power and Q=It for the second question to find average current. . .
In an AC circuit current and voltage alternate, following a sine wave, therefore power alternates (P=IV). The mean current and mean power is the root mean square current or power of the peak current/power. Ipeak = root2 * Irms.

1)Use the equation E = Pt = 1/2 CV^2

2)Use Q = It
Thanks i am kinda kicking myself now! :s
Original post by rosierm
Ok so really confused as to how i find things like mean power and mean current ?
These are two examples of questions i am stuck on:
1) In experiments to pass a very high current through a gas, a bank of capacitors of total capacitance 50 microF is charged to 30 kV. If the bank of capacitors could be discharged completely in 5.0ms what would be the mean power delivered?
A 9.0 MW
B 4.5 MW
C 110 kW
D 22 kW
2) A camera flashgun uses the discharge of a capacitor to provide the energy to produce a single flash. In a particular flashgun a 4700 microF capacitor is initially charge from a 90V supply.
I calculated the charges stored as 0.423 C and the energy stored as 19J but i am stuck on the next part which is:
iii) the average current which flows if total discharge of the capacitor takes place effectively in 30ms

please see this video for complete solution: https://youtu.be/Ctt3EBOVxt0