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This question already has an answer here:

In the construction of a full wave rectifier, why is there central tapping in the secondary winding of the power transformer? What's the pure reason behind it? If there was no central tapping, what would be the change?

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marked as duplicate by John Rennie, Emilio Pisanty, Qmechanic Mar 19 '13 at 19:57

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

but I'm not satisfied with that answer. – Samama Fahim Mar 19 '13 at 18:22
If you are not satisfied with an answer, please do not re-ask the same question. There are other ways to bring attention to a question. E.g. a bounty. – Qmechanic Mar 19 '13 at 20:02
Cross-posted from – Qmechanic Mar 19 '13 at 21:35
@Qmechanic OK I didn't know that! Sorry! – Samama Fahim Mar 20 '13 at 9:54
up vote 2 down vote accepted

if there was no central tapping, what would be the change?

Consider this circuit diagram, from the answer you're not satisfied with:

enter image description here

There is no "central tapping" so the two diodes are connected in series. In a series connected circuit, the current through each circuit element is identical.

Now, note that D1 allows only a clockwise current while D2 allows only a counter-clockwise circuit. The only solution that satisfies both constraints is zero current.

So, without the center-tap, there is zero current in the secondary circuit and thus, by Ohm's Law, zero voltage across the resistor R.

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