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what is the voltage across C1?

Discussion in 'Electronics Homework Help' started by charmcaster.engg, Jan 20, 2015.

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  1. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    If C1, a 4.7 [​IMG]F capacitor, and C2, a 3.3 [​IMG]F capacitor are in series with 18 Vdcapplied, what is the voltage across C1?
    Frequency is not mentioned.
     
  2. davenn

    davenn Moderator

    13,880
    1,964
    Sep 5, 2009

    because DC voltage doesn't have a frequency

    google capacitors in series
     
  3. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    Then how to find Xc?
     
  4. davenn

    davenn Moderator

    13,880
    1,964
    Sep 5, 2009
    There is NO Xc ( capacitive reactance) ..... again ... Its DC voltage

    did you google voltage across capacitors in series ?
     
  5. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    V=Vc1+Vc2 and Vc1=Q/C1, Vc2=Q/C2. I find out total capacitance using C1*C1/C1+C2=1.94uF. Then Q=C*V=34.92. n then Vc1=Q/C1=7.42.
    Am I right?
     
  6. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Correct, but there is no need to calculate the charge Q. Just recognize that the charge is equal in both capacitors. C=Q/V, Q1=Q2, C1∙V1=C2∙V2. The voltage law gives V1+V2=18.

    So just solve these two equations for V1: C1∙V1=C2∙V2 & V1+V2=18

    V2=(C1/C2)V1, (1+C1/C2)V1=18, V1=18/(1+4.7/3.3) = 7.425
     
  7. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    Thanks!
     
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