Can I get help with an inductance problem?

The current is irrelevant here. The self-inductance of a long solenoid is equal to [math]\mu_0 N^2 \pi r^2 l[/math], where N is the number of turns per unit length. Calculating with your provided values returns a self-inductance of 0.3553 mH. I can provide further assistance if needed.

>>8815381
Unrelated to inductance..(somewhat). Hopefully you can help.

I have a yes/no question asking if it is possible to calculate the speed of light using only (forgive me, but I do not know how to print these characters with a keyboard, so I will write them phonetically) mew-knot, or epsilon-knot.

I know the correct answer is Yes, but why?

This may sound uncreative, but my professor never went over light....our units never covered light. We covered electricity/magnetism only...We have worked on the properties of charged materials and particles only. It is lost upon me how I would use the two aforementioned universal constants to calculate the speed of light.

>>8815554

This is a pretty complex question.

Light is described by Maxwell's Equations. If you solve these equations in the absence of any charge, one solution is a plane wave traveling at c. Epsilon-naught and mu-naught are important parts of the equations.

File: circuit.png (7KB, 324x164px) Image search: [Google]

7KB, 324x164px

>>8815819
Last two questions (Q1)

I have a circuit, shown in pic. The circuit starts discharged, with switch in position b, and then is thrown to switch A. It remains at position A for "a long time". It is then thrown back to position B.

Official wording: How much time elapses before the voltage across the inductor drops to 13V ?

My work: I have two equations: rise and decay of current. Decay of current is applicable here...I have, i(t) = ((emf)/(R))(e^ (-t/tau))

I know a fair bit of math, so substituting in for Voltage or getting rid of the exponential stuff is no issue. My problem is more philosophical - what numbers am I inputting for the emf and R. The resistance/emf of the circuit when I have switch at position A or B?

File: circuit2.png (19KB, 323x437px) Image search: [Google]

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>>8815819
Q2

Simply put, IDK what I'm doing here. I mean I know what magnetic flux is, but...I just...idk.

My first thought is to calculate the magnetic field at the distances 2 cm away and 9.5 cm away, and then integrate across the 10 cm side, much like shells in calculus..However, as appealing as brute forcing is - because it gets me the answer, an appealing thought - I am hesitant to do so because the physics class I am taking requires only basic calculus, and none of the work, or equations, are as tough as shells, none take as much work as shells....shells just seem very out of place, and it smells like the wrong ~ optimal~ method of solution.

>>8815299
[math]L = \frac{\mu_0 N^2 A}{L}[/math]


>>8815554
assuming you know Maxwell's equations, when you take [math]\nabla\times(\nabla\times E)[/math] and likewise for the magnetic field in the presence of no charges, after some vector identity manipulation you get a wave equation with velocity [math] c = 1/\sqrt{\mu_0\epsilon_0}[/math]

>>8816109
from Ampere's law the B field is [math] B = \frac{\mu_0 I}{2\pi r}[/math], then since the [math] r [/math] direction is the width, we have:
[math] \phi = \frac{\mu_0 I h}{2\pi}\displaystyle\int_{d}^{d + w} \frac{dr}{r}[/math] where d is the distance from the wire to the loop (so 2 cm here) and w is the width of the loop.

>>8816102
long time current is I0=13.9V/13Ω
decay is i(t)=I0*(e^-t/(L/R))
find t for i(t)=13.9V/1143Ω

>>8816215
Thanks.

>>8816127
Thank you. I was missing the height aspect of the problem, I had to think of it as a toroid instead of a solenoid....

Bless all of you in this thread.

>>8816215
>find t for i(t)=13.9V/1143Ω
I think it says 13V. The current that produces 13V across 1143Ω. 4ms after the kilovolt spike.

OP Here again

>>8816127
>>8815819
>>8815381
>>8816215

You all are evidently more knowledgeable than me, and farther ahead in your educations...I will be finishing my Intro to Physics (calc-based) courses this May. I have a B+ in the class...currently I'm on track to become some sort of engineer. Probably electrical, but I might head down nuclear, or mechanical of electric gets too tough.

Are the courses I have ahead of me more challenging than this? Not in a difficulty sense, but in a time sense. I worked very hard, more hard than I ever did in high school, for that B+. I know this is a very privileged freshman thing to say, but jeez....i worry that the *real* (as in, smart) engineers are getting A+'s in this class and that I might as well drop now.