Confused about solenoid radius from this site

In summary, the radius is the outer radius minus the inner radius. If there is only one layer of coil, the radius is the outer radius - the inner radius.
  • #1
So I was reading a thread on PF talking about the radius of a solenoid and Bob S answered with a link:
Bob S said:
This equation for the on-axis field is exact both inside and outside the solenoid:

http://www.netdenizen.com/emagnettest/solenoids/?solenoid

You can add more layers at the ends.

Bob S

On that site, it states that the Radius = the outer radius - the inner. It doesn't make sense. What happens when there is only one layer of coil and the outer radius (OR) is basically the inner radius (IR). That would create a larger magnetic field than if I had multiple layers of coils and the OR > IR which would then create a smaller one. I don't understand why.
 
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  • #2
On that site, it states that the Radius = the outer radius - the inner.
Where?
What happens when there is only one layer of coil and the outer radius (OR) is basically the inner radius (IR).
Even in that case, your cables have a finite width.

You can probably consider this equation in the limit r1 -> r2, and get a simpler equation for the case where the difference between both is not significant.
 
  • #3
mfb said:
Where?

In the equation where the denominator is 2(r2-r1). So I'm assuming that the more layers of coils you have, the greater r2-r1 is and therefore less magnetic fields. Which I don't get. I thought the more coils you have, the greater the magnetic field.
 
  • #4
Careful, the radii are used in the logarithms as well. It is not clear which effect will dominate if you don't calculate it.

"More coils" would also increase n (more windings) or I (more current), cancelling this effect. More coils give a higher field strength.
 
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  • #5
mfb said:
Careful, the radii are used in the logarithms as well. It is not clear which effect will dominate if you don't calculate it.

Oh...Whoops. Thank you. I can't believe I forgot about that.
 

1. What is a solenoid radius?

A solenoid radius is the distance from the center of a solenoid to its outermost edge. It is typically measured in units of length, such as meters or centimeters.

2. How is a solenoid radius calculated?

The solenoid radius can be calculated using the formula r = (N * l) / (2 * pi), where N is the number of turns in the solenoid, l is the length of the solenoid, and pi is the constant value of 3.14.

3. What is the significance of the solenoid radius in a magnetic field?

The solenoid radius determines the strength of the magnetic field produced by the solenoid. A larger radius results in a stronger magnetic field, while a smaller radius results in a weaker magnetic field.

4. Can the solenoid radius be changed?

Yes, the solenoid radius can be changed by altering the number of turns or the length of the solenoid. It can also be changed by using materials with different magnetic properties, such as using a ferromagnetic material to increase the strength of the magnetic field.

5. Why is the solenoid radius important in practical applications?

The solenoid radius is important because it affects the efficiency and functionality of devices that use solenoids, such as electromagnets, electric motors, and speakers. Choosing the appropriate solenoid radius is crucial for achieving the desired results in these applications.

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