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For each homework question and lab report we will make a post, this will probably contain a few tips on what the problems are about and how to solve them. If you are stuck on something then instead of emailing us directly you should post a comment in reply to the relevant post. We will try to guide you through tough points and help you understand the problems and the concepts behind them.
Thursday, September 23, 2010
Chapter 18, Problems 10-12
Problems with resistors and capacitors, from Section 18.5.
5 comments:
Karole
said...
For part b I keep getting the incorrect answer. I am taking the Emf which is 27V and multiplying it but e^-1. Then I'm taking that value and multiplying it by the capacitance given in the problem which was 15 microfarads. This gives me the charge after 1 time constant, no?
For number 12 part a, the equation i used was .8 (because i had 80% of the capacitance left in my problem) = 1-e^(-t) because RC = time constant = 1 second. I keep getting 1.609 seconds and it's wrong. Please help.
In Q12, you're dealing with a capacitor which is initially charged. Go back to page 607 and find the equation for the discharge of an initially charged capacitor. (And I assume you meant that your problem asks for the time when 80% of the charge remains, not 80% of the capacitance.)
5 comments:
For part b I keep getting the incorrect answer. I am taking the Emf which is 27V and multiplying it but e^-1. Then I'm taking that value and multiplying it by the capacitance given in the problem which was 15 microfarads. This gives me the charge after 1 time constant, no?
That previous question was for number 10. Sorry.
The capacitor is charging, so Fig 18.16 and Eq. 18.7 show what is happening.
For number 12 part a, the equation i used was .8 (because i had 80% of the capacitance left in my problem) = 1-e^(-t) because RC = time constant = 1 second. I keep getting 1.609 seconds and it's wrong. Please help.
In Q12, you're dealing with a capacitor which is initially charged. Go back to page 607 and find the equation for the discharge of an initially charged capacitor. (And I assume you meant that your problem asks for the time when 80% of the charge remains, not 80% of the capacitance.)
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