nix85
Member level 3
Formula for magnetic field strength H = amp x turns / length is well known, but it leads to misleading results. Not to calculate manually we can use this online calculator
https://www.omnicalculator.com/physics/solenoid-magnetic-field
First of all this formula does not take into account the diameter of the coil. It is not the same if coil has 1cm radius or 10cm, of course, bigger the radius less flux density for same field strength.
Second and key point is that as we decrease the length of the coil field is supposedly getting proportionally stronger. For example, if we enter just 1 turn, current of 1mA but we decrease the thickness down to 1 millionth of a cm, that is, 0,0000001 cm, we supposedly get a field of ~1,25T.
Now, we sure don't expect that such miscroscopic coil would extend it's field anywhere outside it's microscopic dimensions. It might be 1.25T but only on the microsopic level which is not implicated by this formula.
I am asking cause i am trying to make a 0.4T or stronger field inside a 4cm diameter air core coil. But with this formula as only reference i can't be sure of best combination.
For example if i take 25 meters of 1mm thick wire and wind 50 turns of it all in one level and push 20A into it, according to the formula, field strength in the center of the coil will be ~1.3T.
I am highly skeptical that this is realistic, again maybe it is on a minute scale if coil radius is very very small.
My intuition tells me to use 100 meters of 2mm wire all wound in same plane in Tesla bifilar fashion to get bit more juice out of it. I roughly estimate this would be ~150 turns.
According to formula above with 20A current, field in the center of this coil should be ~1.9T. But is it really?
What do you think/know.
https://www.omnicalculator.com/physics/solenoid-magnetic-field
First of all this formula does not take into account the diameter of the coil. It is not the same if coil has 1cm radius or 10cm, of course, bigger the radius less flux density for same field strength.
Second and key point is that as we decrease the length of the coil field is supposedly getting proportionally stronger. For example, if we enter just 1 turn, current of 1mA but we decrease the thickness down to 1 millionth of a cm, that is, 0,0000001 cm, we supposedly get a field of ~1,25T.
Now, we sure don't expect that such miscroscopic coil would extend it's field anywhere outside it's microscopic dimensions. It might be 1.25T but only on the microsopic level which is not implicated by this formula.
I am asking cause i am trying to make a 0.4T or stronger field inside a 4cm diameter air core coil. But with this formula as only reference i can't be sure of best combination.
For example if i take 25 meters of 1mm thick wire and wind 50 turns of it all in one level and push 20A into it, according to the formula, field strength in the center of the coil will be ~1.3T.
I am highly skeptical that this is realistic, again maybe it is on a minute scale if coil radius is very very small.
My intuition tells me to use 100 meters of 2mm wire all wound in same plane in Tesla bifilar fashion to get bit more juice out of it. I roughly estimate this would be ~150 turns.
According to formula above with 20A current, field in the center of this coil should be ~1.9T. But is it really?
What do you think/know.