0:23 "When a current flows through a coil, it generates magnetic flux around the coil. When the current tries to increase or decrease, then the flux generates a secondary EMF."

Unclear.

- Is the initial flux considered the 'primary' flux?
- Is the initial flux considered a form of EMF?
- Is the "secondary EMF" considered a form of flux?
- Do both exist simultaneously?

Thx

 

The generated voltage is proportional to the time rate of change of the current. The magnitude of the current is irrelevant, it is only the time rate of change. The constant of proportionality is the inductance L. If the current is represented by a sinusoidal function, the the secondary EMF is represented by the derivative of the sinusoidal function. It is known the that the derivative of the sine is the cosine and it leads the sine by 90 degrees.

 

"emf" is as he is using it means electromotive force, which is measured in volts. Vernacular use would have 'emf' mean electromagnetic field.

 

The generated voltage

i couldn't find anything in the video about a generated voltage.
i understand about the 90 degrees.

"emf" is as he is using it means electromotive force, which is measured in volts. Vernacular use would have 'emf' mean electromagnetic field.

so the generated EMF is a voltage?

i don't understand how these are answers to my questions above.

thx

 

Well flux and EMF are not the same thing. EMF is measured in Volts. EMF is generated ANY time there is a change in current. This includes the first time there is a change AND every time there is a change. The changes can be discrete or continuous - it does not matter. The flux is the surface integral of the normal component of the magnetic field passing through the surface. The SI unit of measurement for flux is the Weber (Wb) and it has units of volt⋅seconds. You cannot compare two things that have different units; it just can't be done.

In my estimation the concept of primary EMF and secondary EMF is a meaningless distinction. EMF is EMF period.

Current flowing in the coil creates flux, and changing current creates EMF

Are you familiar with surface integrals?

 

In my estimation the concept of primary EMF and secondary EMF is a meaningless distinction. EMF is EMF period.

I agree with that assessment.
I see no distinction between the two.
In all cases the coil EMF (voltage) is generated by the change in magnetic flux.