Why a transformer cannot use DC (Ampere's law)?

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A transformer cannot use direct current (DC) because a constant magnetic field in the primary winding does not produce a changing magnetic flux in the core. According to Ampere's law, the voltage in the secondary coil is dependent on the rate of change of magnetic flux. Without this change, there is no induced voltage in the secondary coil, resulting in no current flow. Therefore, a generator must spin to create a changing magnetic field, which is essential for inducing current. This principle underlines the fundamental operation of transformers and generators.
kekkeroo
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A direct current in the primary winding results in a constant magnetic field going through the center of the coil. If we have a magnetic core and a second winding, why doesn't the magnetic flux going through the core result in a current in the secondary coil, as well, according to Ampere's law?
 
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The short answer is that the changing current in the primary causes a changing flux in the core.
The voltage in the secondary is proportional to the rate of change of flux in the core.
No change in core flux, implies no secondary voltage, so no secondary circuit current.
https://en.wikipedia.org/wiki/Transformer
 
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kekkeroo said:
why doesn't the magnetic flux going through the core result in a current in the secondary coil
Why do you need a generator spinning to have current in its coil?
 

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