# What is the induction at infinity ?

totalnewbie
What is the induction at infinity ?
I told teacher it to be 0 but she disagreed.

Using the formula for calculating induction and substituting big distances into the formula gives me also 0.
Is my teacher stupid ?

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Doc Al
Mentor
What is the induction at infinity ?
Induction of what? I have no idea what that graph represents. Please present the entire question with all needed background info.

totalnewbie
Induction of what? I have no idea what that graph represents. Please present the entire question with all needed background info.
Magnetic induction.
It is produced by homogeneous solenoid.

totalnewbie
Any feedback ?

Doc Al
Mentor
Are you asking about the magnetic field outside of a solenoid as distance goes to infinity?

What formula did you use? What does that graph represent?

totalnewbie
Are you asking about the magnetic field outside of a solenoid as distance goes to infinity?

What formula did you use? What does that graph represent?
I had a solenoid and its lenght was 0,222 meters. The diameter of the solenoid was 120 mm.
My goal was to measure the magnetic induction of the solenoid at solenoid axis. The current that runs through solenoid is a sinusoidal AC.
The coil was used to measure magnetic induction. At the axis
the voltmeter shows me that at the center of solenoid the voltage is about 0,40 Voltage. Moving away from the point at center reduces the voltages. In other words about 12 cm away from the center shows me that the voltage is 0,18 V. Why does moving away from the center point at solenoid reduces voltages ?
The formula for calculating magnetic induction at certain distances from the center point was:
induction = (l/2 - x)/sqare root((l-2x)^2+D^2) + (l/2 + x)/sqare root((l+2x)^2+D^2) where l is length of solenoid and D is diameter of solenoid.
The condition l >> D is not satisfied.

I was told that magentic field was homogenous. Why does the voltages reduces if magnetic field is homogenous ?

Let me put my problem into other words.
Let's discuss what happens to solenoid when current runs through.
In physics, the term solenoid refers to a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electrical current is passed through it. As for solenoid I was using to do my experiments in order to calculate the magnetic field I want to ask the following.
Because l << D is not satisfieid I suppose that the current which flows through loop of wire is the same everywhere where the current passes.
If we look at this solenoid, which is 20 cm lenght. Is it right to say that choosing one point on this solenoid's wrap produces different induction current if we go away from the point we consider the situation ?

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totalnewbie
Any help within 3 hours would be highly appreciated.

Doc Al
Mentor
I had a solenoid and its lenght was 0,222 meters. The diameter of the solenoid was 120 mm.
That's not much of a solenoid--generally solenoids have a length much greater than the diameter, assuring a relatively homogenous field inside the solenoid.
My goal was to measure the magnetic induction of the solenoid at solenoid axis. The current that runs through solenoid is a sinusoidal AC.
The coil was used to measure magnetic induction. At the axis
the voltmeter shows me that at the center of solenoid the voltage is about 0,40 Voltage. Moving away from the point at center reduces the voltages. In other words about 12 cm away from the center shows me that the voltage is 0,18 V. Why does moving away from the center point at solenoid reduces voltages ?
Your solenoid is only 22.2 cm long--moving 12 cm from the center takes you outside the coil!
The formula for calculating magnetic induction at certain distances from the center point was:
induction = (l/2 - x)/sqare root((l-2x)^2+D^2) + (l/2 + x)/sqare root((l+2x)^2+D^2) where l is length of solenoid and D is diameter of solenoid.
The condition l >> D is not satisfied.

I was told that magentic field was homogenous. Why does the voltages reduces if magnetic field is homogenous ?
The magnetic field is homogenous inside a solenoid--that's not what you have here. You need to be away from the edges, for one thing. Take a look at the http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html" [Broken]--your setup is partway between loop and solenoid.

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