Defibrillator discharges. need to find time constant

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Homework Help Overview

The discussion revolves around the operation of a defibrillator, specifically focusing on the electrical properties of the capacitor and resistor involved in its discharge process. The original poster presents a series of questions related to the time constant, charge remaining on the capacitor, total charge delivered, and average current during the discharge.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the time constant using the formula R*C but finds the result unexpectedly small. They seek clarification on how to interpret this value and its relevance to the subsequent questions.
  • Participants discuss the calculation of the time constant and its implications for the problem, with one participant noting a misunderstanding regarding the unit of microfarads.
  • Questions arise about the appropriate equations to use for calculating the charge remaining on the capacitor and the total charge delivered to the patient.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the time constant and its application to the problem. Some guidance has been offered regarding the equations that may be relevant for the calculations, but no consensus has been reached on the overall approach.

Contextual Notes

There appears to be confusion regarding the units of capacitance, which may affect the calculations. The original poster is also navigating multiple parts of the problem without a clear resolution on how to proceed with each question.

gujrichick
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A defibrillator uses a capacitor to deliver a large current to a person needing heart stimulation. Assume that the capacitance used is 60microfarads and the resistor it discharges through is 220 ohms. the defibrillator is charged up to 5 kiloVolts and it is discharged through a patient for 1.0 millisecond.

a) What fraction of the time constant is 1.0 millisecond?
b) How much charge is left on the capacitor after the 1.0 millisecond?
c) Find the total charge delivered to the patient.
d) Determine the average current delivered to the patient.'

I used time constant=R*C to find the time constant but it comes out to be smaller than 1.0ms, which does not make sense. I just need to know which equations to use to get the answers right.

Please help. And Thanks to whoever helps!
 
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Welcome to PF!

gujrichick said:
A defibrillator uses a capacitor to deliver a large current to a person needing heart stimulation. Assume that the capacitance used is 60microfarads and the resistor it discharges through is 220 ohms. the defibrillator is charged up to 5 kiloVolts and it is discharged through a patient for 1.0 millisecond.

a) What fraction of the time constant is 1.0 millisecond?
…
I used time constant=R*C to find the time constant but it comes out to be smaller than 1.0ms …

Hi gujrichick! Welcome to PF! :smile:

What did you get for the time constant? :confused:
 
Hi,

I got 1.32*10^-5 seconds as my time constant.. and I don't understand how I would get a fraction from that or how that would help me answer the other questions.
 
Hi gujrichick! :smile:

(try using the X2 tag just above the Reply box :wink:)
gujrichick said:
Hi,

I got 1.32*10^-5 seconds as my time constant.. and I don't understand how I would get a fraction from that or how that would help me answer the other questions.

I get 220 Ω times 60 10-6 F = 1.32 10-2 s
 
oh! I know what I did wrong now, I thought that micro was -9 instead of -6.
Thanks!

but which equations should I use for the other parts? I think for part c I can use C=Q/V and find the total charge. and for d I can do V=IR. But what about part b? Do I use Q=CVe^(-t/RC)? And plug in 1ms for t?
 

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