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# transformer conservation of power

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lets say we have a transformer, on the left side, it is 220 v and on the right side, it is 10 v. we know that power is conserved meaning power on left is equal to right (ignoring loss). I understand how voltage is stepped up or down (induced emf on the other side, if there are more coils, it will produced more emf and so it will stepped up, vice versa), but how does it actually make the current low or high (or adjust), to make the power still equal?

In a perfect transformer run in forward mode, the change in secondary current exactly ballances the change in primary current to keep the magnetic flux the same.

This means the effective current going around the core in each of the primary and secondary must be the same but in opposite direction. The transformer only sees the current going around the core. The multiple turns of a winding only make it look like more current overall going around. To the core, 13 turns of 1 A each is the same as 26 turns at 1/2 A each. The same overall current is still circling the core.

The current that actually flows thru each winding from the external circuit point of view is the current thru each winding since they are effectively in series. The external current is therefore inversely proportional to the number of windings.

Let's say your transformer has 100 A circling the core. That might be 880 turns on the primary, for 114 mA thru the primary from the outside point of view. In this case, the secondary would have only 44 turns. For the ideal case, this would also have to produce 100 A circling the core. Since each turn only contributes 1/40 of that, the current thru the secondary wire needs to be 2.5 A.

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