positive current enters both windings at the marked terminals, the MMFs of the two windings add. Since the secondary voltage depends on the core flux φ 0, it must be clear that the flux should not change appreciably ifE s is to remain essentially constant under normal loading conditions. With the load connected, a current I s will flow in the secondary circuit, because the induced EMF E s will act asa voltage source. The secondary current produces an MMF N sI s that creates a flux. This flux has such a direction that at any instant in time it opposes the main flux that created it in the first place. Of course, this is Lenz ’s law in action. Thus the MMF represented byN sI s tends to reduce the core flux φ 0. This means that the flux linking the primary winding reduces and consequently the
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