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4 replies to this topic

### #1 Ventum

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Posted 18 March 2009 - 12:23 AM

If people can list algebra based inductance equations for this I would be grateful.
Specifically I need to know the equation for inductance in a solenoid and loop.
Also an brief explanation of Right hand rule in a solenoid.
Hey, its worth a shot.
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### #2 rookie1ja

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Posted 18 March 2009 - 12:43 AM

see and act as per point 3 of this forum's rules

3. Show how far you've gotten with your problem and what it is you're stuck on.

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### #3 Ventum

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Posted 18 March 2009 - 01:10 AM

Very well, @=theta
the formula has something to do with @
but the one for solenoid is uh uh ???
i know the right hand rules for most things just fuzzy on solenoids.
my point in the wording of the question was to prove that i understand most things, need help on certain parts.
for ex.
If the solenoid with diameter 15.5cm has 505 loops and it takes 2.77ms to spin from perpendicular with a mag field to parallel, with a V=.166 how strong is mag field?
i don't know what to do with the 505?
i wont round out everything because of decimals
i have .166=((?)/.00277)*((.0775^2)*(pi))

.166/((.0775^2)*(pi))=((?)/.00277)
(.00277)*(.166/((.0775^2)*(pi)))=?
but the answer i get for ? is incorrect

i am assuming the number of loops matter but i would like a general equation for solenoid and straight wire/circuit i have been working w/o a general equation for a while.
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### #4 Yoruichi-san

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Posted 18 March 2009 - 02:33 AM

I assume this is okay since your HW doesn't require you to derive the expression:

For an uniformly wound solenoid having N turns and length l, that satisfies l>>r (radius of the windings), and assuming the core of the solenoid is filled with air, B is magnetic field, u0 is the permittivity of free space, @ is the magnetic flux, I is the current, A is the cross-sectional area:

For a closely spaced coil, the induced electromagnetic field (emf), according to Faraday's Law is related to the negative time rate of change of magnetic flux, which should be proportional to the source current in the circuit. The proportionality constant, L, is the inductance.

Induced emf=-Nd@/dt =-LdI/dt

-> L=N@/I

The magnetic field in a solenoid is: B=u0NI/l

-> @=BA=u0NAI/l

-> L=N@/I=u0N2AI/l

The right-hand rule tells you which direction the induced magnetic field will be pointing. If you point your thumb in the direction of the current then your fingers curve around in the direction of the induced magnetic field.
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### #5 Ventum

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Posted 18 March 2009 - 04:03 AM

Thanks so in the above problem i would multiply my final expression by 505? and the right hand makes sense thank you.
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