- #1

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## Main Question or Discussion Point

Hello,

I have seen that biot savart's law works for infinitely narrow wires:

"The formulations given above work well when the current can be approximated as running through an infinitely-narrow wire."

When I wanted to derive the magnetic field of a solenoid, I had to do this substitution:

##n_o = N/L##

## k = n_o dx ##

Where k is the number of turns per dx.. But shouldn't K be an integer? so I can substitute it in the formula for circular coils. That means I have infinite number of turns and turn density of something like ## \frac{a}{dx} ## where a is an integer.

Is there is something wrong or that this is the idealization that we do to the solenoid? Wouldn't it be way off the correct value?

If you want the proof, http://nptel.ac.in/courses/122101002/downloads/lec-15.pdf

Page 8, Example 9.

Thank you in advance.

I have seen that biot savart's law works for infinitely narrow wires:

"The formulations given above work well when the current can be approximated as running through an infinitely-narrow wire."

When I wanted to derive the magnetic field of a solenoid, I had to do this substitution:

##n_o = N/L##

## k = n_o dx ##

Where k is the number of turns per dx.. But shouldn't K be an integer? so I can substitute it in the formula for circular coils. That means I have infinite number of turns and turn density of something like ## \frac{a}{dx} ## where a is an integer.

Is there is something wrong or that this is the idealization that we do to the solenoid? Wouldn't it be way off the correct value?

If you want the proof, http://nptel.ac.in/courses/122101002/downloads/lec-15.pdf

Page 8, Example 9.

Thank you in advance.