# Homework Reassurance needed

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

1. ### spidermanmov Thread Starter New Member

Oct 7, 2009
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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
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This is a simple calculus question. Can you do simple calculus?

3. ### spidermanmov Thread Starter New Member

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

Feb 12, 2009
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