Homework Reassurance needed

Discussion in 'Homework Help' started by spidermanmov, Oct 8, 2009.

  1. spidermanmov

    Thread Starter New Member

    Oct 7, 2009
    i have asked to do a question but i am not sure if it is right, the question is:a 35uF capacitor is charged to 500v it is then connected to a 20Mohms resistor, estimate time taken for charge to drop to 10v?my answer was around 2hrs, is this about right?thanks
    the reaon i got to 2 hours was i first found out my time constant which is t=rc which is time = resistance x capacitance and my answer was 700, then i created a time curve with my time constant in 700sec increments along bottom and current up the side, my highest current value i used was 25uA because i used i = V/R. USING OHMS LAW i could find out voltage at 25ua, and as time goes on the current level droppped as did voltage, as on this curve i got 10v when time reached about 7350 secs ( 2 hrs ), am i right?
    Last edited: Oct 8, 2009
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    This is a simple calculus question. Can you do simple calculus?
  3. spidermanmov

    Thread Starter New Member

    Oct 7, 2009
    what formula would you have used? how different would your way be compared to what i have done?
  4. JDT

    Well-Known Member

    Feb 12, 2009