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No Idea how to work this out! - Charging and discharging an iPod

  1. Jul 6, 2012 #1
    No Idea how to work this out! -- Charging and discharging an iPod

    1. The problem statement, all variables and given/known data

    It takes about 5 hours for a fully charged ipod nano to run out of power when its screen is left on and all other functions are switched off. Subsequently, it takes about 90 minutes to recharge the ipod from a charging unit with a 5V and 500mA output. The same ipod takes about 24hours to run out of power when only the audio function is used

    a) calculate the power consumption of the screen and audio output seperately

    b) calculate when the power will run out if the user switches on the screen for 10 seconds every 3mins (i.e. about once every track) assuming the ipod is fully charged at the start.

    2. Relevant equations



    3. The attempt at a solution

    I dont know where to start with this question been stuck on it for hours and cant get anything from it :( please help!!
     
  2. jcsd
  3. Jul 6, 2012 #2

    berkeman

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    Staff: Mentor

    Re: No Idea how to work this out! -- Charging and discharging an iPod

    You are given complete information about the charging situation. How much power is used to charge the iPod? How much energy is stored in the battery during the charging time?
     
  4. Jul 6, 2012 #3
    Re: No Idea how to work this out! -- Charging and discharging an iPod

    is the power of the iPod

    90*60 = 5400joules?
     
  5. Jul 6, 2012 #4

    berkeman

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    Re: No Idea how to work this out! -- Charging and discharging an iPod

    What is that? 90 minutes * 60 seconds/minute ?

    What is the equation for power P in terms of voltage V and current I ?

    What is the equation for Energy E in terms of power P and time t ?
     
  6. Jul 7, 2012 #5
    Re: No Idea how to work this out! -- Charging and discharging an iPod

    so the formula for power

    P= I . V ?? ----> 5 x 0.5 = 2.5 watts?

    E= P . t -----> 2.5 x (5*60*60) = 45000 ?

    then I'm unsure on what to do?
     
  7. Jul 9, 2012 #6

    berkeman

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    Re: No Idea how to work this out! -- Charging and discharging an iPod

    Good! Be sure to carry units along in your equations, so your E = 45000J.

    So what is the discharge power if it takes 24 hours to discharge that energy?
     
  8. Aug 9, 2012 #7
    Re: No Idea how to work this out! -- Charging and discharging an iPod

    would it be

    45000J/ 24*60*60??
     
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