# How to tell the magnetic flux a certian distance from a solenoid?

• Nightsinger
In summary, the conversation revolves around a coursework problem related to predicting the height of a jumping ring in an experiment using Lenz's law. The main issue is determining the magnetic field strength at a certain distance from a solenoid, with different formulas and variables being considered. The individual is seeking clarification and insight on how to approach the problem.

#### Nightsinger

How to tell the magnetic flux a certian distance from a solenoid??

This is about a coursework problem that I've been trying to figure out for the past few weeks.

This is my context, for those wanting to know
i'm trying to predict the high of the ring, in the jumping ring experiment. For those of you who have no idea what that is, it basically takes advantage of Lenz's law, see here: http://www.physics.brown.edu/physics/demopages/Demo/em/demo/5k2030.htm
The voltages that i am working with are no where near high enough to cause the ring to jump, the ring more levitates to a certian height along the extended iron core.
This happens when the force due to the magnetic field equals that of gravity.

My problem
I can't really get my head around working out the magnetic field strength a certian distance outside of the coil (not from the side of the coil but from the end)

The attempt at a solution

at first i thought that applying the siot-savart law would offer me an answer.

B=μ0Ilsinθ/4πr2

where r is the distance. sinθ the angle. I the current. And μ0 the permibibility of free space.

if i took θ to be 90 degrees. as the coil is 90 degrees the plane of the core, as its twisting around it. this would eliminate sinθ as it equals 1.

Therefore B = μ0Il/4πr2

my problem now is n defining l, is it the circumferance of the coil or the total length of line in the coil. I'm generally havng problems with this law, what is this length meant to mean. and can the number of turns be factored into the equation.Additionally, I would have to add a μr term to include the relative permeability of the core

I looked through my book and found an additional formula for a flat circular coil:

B = μ0IN/2 times r2/(r2times x2)3/2

where r is the radius of the coil. x the distance. N the number of turns. I the current. And μ0 the permibibility of free space.

This seems to make more sense but my coil is a long
solenoid, how do they differ? can this equation still work.

I would really appreciate any insight that anyone can give for this problem. Its really been getting to me, and my teacher seems more concerned over other things than over the problems I'm having with my coursework. despite that, i have to get to understand this.

## 1. How does the distance from a solenoid affect the magnetic flux?

The distance from a solenoid does not directly affect the magnetic flux. However, the strength of the magnetic field decreases as the distance increases due to the spreading out of the field lines.

## 2. How do you measure the magnetic flux at a certain distance from a solenoid?

The magnetic flux can be measured using a magnetic field sensor, such as a Hall probe, placed at the desired distance from the solenoid. The sensor will detect the strength of the magnetic field at that location.

## 3. What factors can affect the accuracy of measuring magnetic flux from a solenoid?

The accuracy of measuring magnetic flux from a solenoid can be affected by factors such as the sensitivity and calibration of the magnetic field sensor, the presence of other magnetic fields in the area, and the quality and uniformity of the solenoid's construction.

## 4. Is the magnetic flux the same at all points along the solenoid's axis?

No, the magnetic flux is not the same at all points along the solenoid's axis. It is strongest at the center and decreases as you move away from the center towards the ends of the solenoid.

## 5. Can the strength of the magnetic flux from a solenoid be increased by increasing the distance from the solenoid?

No, increasing the distance from the solenoid will decrease the strength of the magnetic flux due to the spreading out of the field lines. The only way to increase the strength of the magnetic flux is by increasing the current or number of turns in the solenoid.