(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Suppose your physics lab class lasts for a very long time - long enough for you to wind a semi-infinite solenoid. (That spool of copper wire is the gift that keeps on giving.) What is the on-axis magnetic field at the end of the solenoid closest to you (ie., not at infinity)?

2. Relevant equations

1. i think: http://www.netdenizen.com/emagnet/solenoids/Image34.gif

2. mu(0)*n*i

3. http://img.sparknotes.com/figures/2/288a4611d51a3a7ce874c4a906855ac9/latex_img33.gif

3. The attempt at a solution

- well i thought that i could use formula 1, but there is a L term in that, and i thought that it wouldnt work because this is a semi-infinite solenoid.

- the formula from spark notes (4pi*i*n)/(c) , i had never ever seen before so i was scared to go for it.

i dont really know how to apply any of these formulas to the question.

+++++++

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heres a problem from spark notes thats practically the same except it asks to find the other end:

A semi-infinite solenoid is a solenoid which starts at a point, and is infinite in length in one direction. What is the strength of the magnetic field on the axis of the solenoid at the end of a semi-infinite solenoid?

Solution for Problem

To solve this problem, we use the superposition principle. If we put two semi- infinite solenoids end to end, we have an infinite solenoid, and the field strength at any point in the infinite solenoid is (4pi*i*n)/(c) . By symmetry, the contribution of each semi-infinite solenoid is equal, so the contribution of one semi-infinite solenoid must be exactly one half of the magnetic field in an infinite solenoid, or

B = (2pi*i*n)/(c)

This problem displays the power of the superposition principle, which simplifies what would be a complex calculation.

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# Homework Help: Magnetic Fields In Semi-Infinite Solenoid's

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