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Help with question please!

  1. Jan 15, 2012 #1
    A pacemaker stimulates heart tissue with R of 100ohms.
    Pulse amplitude is 1.2 Volts & pulse duration is 0.5ms.
    Stimulates at 70bpm
    Current drain = 2microamps

    Calculate energy delivered to heart from pacemaker at each pulse.

    i got

    P=V^2/R = 0.0144

    Then Energy = Power*time = 0.0144*0.5x10-3 = 7.2x10-6 J

    But do i not need to take into account the current drain?
  2. jcsd
  3. Jan 15, 2012 #2

    jim hardy

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    Science Advisor
    Gold Member

    power P = V X I

    and since I = V/R,
    P= V X (V/R) = V^2/R

    so when you did V^2/R you included current.

    the 2 microamps sounds more like battery drain to me.

    7.2 microjoules 70 times a minute = 8.4 microwatts
    at 2 microamps dictates least 4.2 volt battery?

    anything corroborate here?
  4. Jan 15, 2012 #3
    2µA - It is current drain due to the pacemaker circuitry.

    Im a bit confused, its a past exam question.
  5. Jan 15, 2012 #4
    all the values i gave were all that was given in the question.
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