- #1
sarahwill
- 5
- 0
Hello.
If we assume an ideal transformer, why do we use a.c current in a transformer? I've searched and answers are that we need a changing electric current to produce a change in magnetic flux, using Ampere's law.
However, Faraday's law states that a voltage produced a changing magnetic flux as well. Isn't there a voltage across the primary coil for current to flow, that would cause a changing magnetic flux? I have tried the maths, and deduced the transformer equation.
If the primary voltage V is the negative of the rate of change of magnetic flux -dø/dt multiplied by the number of coils in the primary coil, then V = -Ndø/dt. But this changing magnetic flux would also induce a current in the secondary coil. If v is the secondary voltage, and n the secondary number of turns, then v = -ndø/dt. Taking the ratio of V/v, we have it being the same as N/n. Since it is a voltage, and not the rate of change of voltage that created the magnetic field, we do not need to vary the voltage to produce a changing flux, so even if the voltage was constant, a current would be induced.
So unless I am missing something, a.c is not required to generate magnetic fields. So why does a transformer use a.c? Thanks
If we assume an ideal transformer, why do we use a.c current in a transformer? I've searched and answers are that we need a changing electric current to produce a change in magnetic flux, using Ampere's law.
However, Faraday's law states that a voltage produced a changing magnetic flux as well. Isn't there a voltage across the primary coil for current to flow, that would cause a changing magnetic flux? I have tried the maths, and deduced the transformer equation.
If the primary voltage V is the negative of the rate of change of magnetic flux -dø/dt multiplied by the number of coils in the primary coil, then V = -Ndø/dt. But this changing magnetic flux would also induce a current in the secondary coil. If v is the secondary voltage, and n the secondary number of turns, then v = -ndø/dt. Taking the ratio of V/v, we have it being the same as N/n. Since it is a voltage, and not the rate of change of voltage that created the magnetic field, we do not need to vary the voltage to produce a changing flux, so even if the voltage was constant, a current would be induced.
So unless I am missing something, a.c is not required to generate magnetic fields. So why does a transformer use a.c? Thanks