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  • basic confusions

    Ali.imran

    Member

    Updated: Oct 26, 2024
    Views: 1.0K
    in case of ac ( 3 phase) three lines come from the generation site and neutral wire is not present. we just make a connection with any of these wire , apply it to a device , consider led and apply any ground even the earth itself act as ground, the led turns on but when you connect led to positive terminal of battery and other end to the ground it will not lighten. it will only turn on when the other leg of led is connected to the negative of the same battery.
    Q)why is it so??????
    for ac the charge moves from live wire passes through the led and into the ground thus led turns on.
    the same should be the case with dc, charge from positive should pass through led and into the ground but led doesn't turn on.Why????
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Replies

  • Ali.imran

    Member • Jul 11, 2012

    ii
    to make my questions clear i have uploaded this simulation.
    in fig b for both cases charge moves or should move from positive terminal and eventually should reach ground or negative terminal (just like in fig a )but the led remains off.
    Q)why is it so??????
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  • Ali.imran

    Member • Jul 11, 2012

    ii
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  • Harshad Italiya

    Member • Jul 11, 2012

    Really Interesting question. Anyone here to clear this?
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  • Ali.imran

    Member • Jul 12, 2012

    WELL???
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  • Ramani Aswath

    Member • Jul 12, 2012

    It is simple. Battery is an isolated (floating) power source. Ultimately the charge leaving the battery has to return to the other terminal. Otherwise the circuit is not closed. The AC generator on the other hand, is ground referenced at the point of generation. If you connect a voltmeter between the line and ground it will show full line voltage. If you try a similar exercise with a battery the meter will show zero showing that there is no potential difference between the battery and ground. Current flow requires a potential difference. So the LED remains off.
    However, If you ground the other terminal of the battery then you can light the LED by connecting between ground and the other ungrounded terminal maintaining correct polarity.
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  • Ali.imran

    Member • Jul 12, 2012

    thanks bioramani.
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