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  • Q1. How capaitor acts as a filter ?(reason behind its action)
    Q2. Why capacitors with high capacitance are used at power rails and the one with low capacitance at power dips ?? ( i am asking how to decide which capacitor should be used where )
    Q3. Why capacitor blocks dc current while allows ac current to pass? i know mathematically but want to know physically
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Replies

  • d_vipul

    Member • Sep 26, 2010

    In first question you are asking about high pass filter and low pass filter????
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  • aman_gupta_009

    Member • Sep 26, 2010

    filter to remove ripples
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  • electronicsunzz

    Member • Sep 27, 2010

    My answer to your 2nd question is as follows, we always use a high capacitance content capacitor to high power lines(A.C) and low capacitance capacitor to low electricity mostly on D.C because the power of the A.C lines is very HIGH, so a capacitor needs very high capacitance(i.e high storage of electricity) whereas in D.C situations, it is quite sufficient for a less capacitance of capacitor because the power that deals with D.C is very less(i.e 0.000001watts).
    you may doubt, asking yourself like what happens if we connect a low capacitance capacitor in high power line and a very high capacitance capacitor in D.C power. in that case
    1. when we connect a low capacitance capacitor in high power line, the capacitor blows of due to high power, so the dielectric connectivity opens the circuit and the capacitor is damaged.
    2.when we connect a very high capacitance capacitor in D.C power, that capacitor acts like a open circuit and the current doesn't pass from +ve to -ve. there doesn't exists any damage but the connectivity fails as capacitor acts like an open circuit.
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  • sayandev

    Member • Oct 3, 2010

    For the 1st question- there are two types of filters high pass filter and low pass filter. from passive electronic realization
    we can say that in a low pass filter the capacitor acts as a open circuit for low frequency and the voltage appears across the load and in case of high frequency the capacitor reactance becomes small and acts a short circuit.
    For high pass, the capacitor is connected in series with a resistor,and for high frequencies the capacitor gets short circuited and voltage appears across resistance and for low frequencies the the capacitor acts as an open circuit.
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  • nenuadwani

    Member • Oct 4, 2010

    for the 3rd question---
    the Capacitive Reactance is defined as the measure of Capacitor opposition to the Alternating Cuurent.It is measured in ohms but the frequency plays a major role.
    The Xc = 1/(2*3.14*f*C)
    Xc - Capacitive Reactance in Ohms
    f - Frequency in Hertz
    C - Capacitence in Farad
    For Steady DC the frequency is Zero.So Xc becomes infinity.
    Thats why the Capacitor blocks the DC.

    And if we think more deeply i.e. physically the main construction itself justifies the cause.
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  • sayandev

    Member • Oct 6, 2010

    I think Xc = 1/(j*w*C)
    Now you can say that since in dc frequency(w)=0 therefore Xc= infinite. thus it blocks dc.
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  • gaurav200x

    Member • Oct 9, 2010

    A new Question on Capacitor

    While discussing with someone, I got stumped while the latter asked me a question. A capacitor consists of 2 plates which're filled by a dielectric (mostly air). Hence, a circuit with an RC circuit consists of a resistor and 2 plates of capacitor separated by air between them, or in other words, it is an open circuit.

    Hence, how does the current flow in this open circuit? 😕
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  • nenuadwani

    Member • Oct 9, 2010

    Re: A new Question on Capacitor

    the two plates actually gets charged due to the potential applied . thus an electric field is generated in that space and it can conduct.
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