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Homework Help: Circuit Related

  1. Mar 21, 2005 #1
    So I did a couple circuit questions and these two really have me stumped. One is on paye 613 of The cutnell physics sixth edition number 36. or:

    (one star)
    A light bulb is connected to a 120.0V wall socket. The current in the bbulb depends on the time t according to the relation I=(0.707 A)sin[(314HZ)t]
    a) what is the frequency of the alternating current
    b) determine the resistance of the bulb's filament
    c) what is the average power consumbed by the light bulb?

    from my guesses i believe you use P=I^2R and V/I=R kinds of formulas as well as P=V^2rms/R and P=I^2rmsR to solve bits and pieces but i dont know how to use time and alternating current to deal with this question... in fact i cant even approach this. can someone help me out?

    The other question is 92. page 616 (one star)
    A 3.00 mF and a 5.00 mF capacitor are connected in series across a 30.0V battery. A 7.0 mF capacitor is then connected in parallel across the 3.00 mF capacitor. Determine the volatage across the 7.00 mF capacitor.

    with this question i just generally have no freaking CLUE how to do this other than the capacitors in series and capacitors in paralell equations.... i really dont have any idea... help would be appreciated.
  2. jcsd
  3. Mar 22, 2005 #2
    the second question horrifies me beyond repair.... it looks so easy... but it isnt..? series is in reciprocal and parallel is in regular right....?

    i think i got a 10V drop on the second question over the 7. but i'm not sure......
  4. Mar 22, 2005 #3
    ok solved the second one... that i thought was harder. can someone help wiht the first? i need to know part b and c.
  5. Mar 22, 2005 #4
    A little help...

    For capacitors in series, the Voltage V across each can be found with [tex]V_1 = \frac{q}{C_1}[/tex] and these add up to [tex]30 V = V_1 + V_2[/tex].

    Hope this helps a little :smile:
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