physics question : current and voltage please help meeee?

Question

A defibrillator passes a brief burst of current through the heart to restore normal beating. In one such defibrillator, a 40.0 µF capacitor is charged to 6.0 kV. Paddles are used to make an electrical connection to the patient's chest. A pulse of current lasting 1.0 ms partially discharges the capacitor through the patient. The electrical resistance of the patient (from paddle to paddle) is 230 . What is the initial current through the patient?


if anyone can help me with this question,
i would really appreciate it!
please have mercy n help meeee!

Answer 1

This problem is asking you about the discharge of a capacitor through a circuit consisting of the capacitor and a resistor connected in series. I'll assume you meant that the resistance through the patient was 230 ohms (you didn't specify the units). The voltage across the capacitor will decay exponentially with a time constant equal to 230 ohm * 40 microF:

V(t) = 6.0*10^3 V *exp(-t/((230 ohm)*(4.00*10^-7 F))

V(t) = 6.0*10^3 V * exp(-t/(9.20*10^-3 sec))

The current is given by Ohm's Law:

I(t) = V(t)/R

so in this case,

I(t) = ((6.0*10^3 V)/(230 ohm))*exp(-t/(9.20*10^-3 sec))

I(t) = (26.09 A) * exp(-t/(9.20*10^-3 sec))

The initial current is the value of I(0)

I(0) = 26.09 A

Note that the initial current doesn't depend on the capacitance, just the initial voltage and the resistance.

Answer 2

As the cell ages the internal resistance increases this resistance (r) adds to the circuit resistance R+r therefore the current through the circuit decreases but as far as the cell is concerned the electromotive force (E,M,F.) itl is still producing the EMF of the cell but due to the increase of the internal resistance a potential difference is developed across this resistance and the terminal voltage be reduced by the amount of the Pd .Terminal voltage = E,M,F.- r x I Example a new cell with an EMF of 6 volts and an internal resistance of 1 ohm and a current drain of i amp the Pd across the internal would be 1 volt therefore the terminal voltage would be 5 volts as the cell ages the internal resistance say increased to 2 ohms and the drain was 1 amp the Pd is now 2 volts so now the terminal voltage is only 4 volts

Answer 3

The initial current does not depend on the capacitance, only the voltage and the resistence. Hence the current I = v / R
V is 6000 Volts, R is 230 (Ohms? seems low so check if it is not KiloOhms)
so the answer 26.09 Amper. Wow! a regular fuse would melt with this current.

Answer 4

I agree with the first person. Electrical resistance of 230 sounds way too low. Plus I think 6000 volts at 29 amps would probably give you quite a nasty burn.