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Homework Help: RC Circuits half-life help

  1. Jul 22, 2008 #1
    Hey Everyone, I have a question regarding physics.

    Say you're given an RC circuit with two identical capictors and two identical resistors and that the two resistors are connected in parallel and the two capacitors are connected in parallel and both are used in the circuit.

    How can you figure out what the ratio of the new t 1/2 to the original t 1/2 would be, as in the "half-life"?

    Any help is appreciated. THank you in advance.

    Sorry if I accidently posted this elsewhere, I am new to these wonderful forums and this mistake won't happen again.

    PS: I attempted to use the equations with e and the -t 1/2 but kept getting odd ratios...
  2. jcsd
  3. Jul 22, 2008 #2


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    Staff: Mentor

    Two identical resistors R connected in parallel have an equivalent resistance of R/2.

    Two identical capacitors C connected in parallel have an equivalent capacitance of 2C.

    Does that help? You need to show more specific work if you need more help.
  4. Jul 22, 2008 #3
    Thanks for your reply, berkeman. It does, indeed, help.

    So now that I have this, can i just plug it into this formula:

    where the halflife (t 1/2) = (ln2)RC and that I derived from V(1/2)/Vi = e^((-t1/2)/RC)

    so that the original equation is just that, t1/2 = RC ln2 and the new equation is the same since R/2 times 2C is equal to RC?

    So, to summarize, wouldn't the original and the new half life be the same?
  5. Jul 22, 2008 #4


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    Staff: Mentor

    If I understand the question correctly, then yes, the time constant would stay the same.
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