Solving eqn with given B.C's: d(r(dV_z/dr))/dr = 0, V_z=0 on

aligee

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Aug 7, 2008
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Hi everyone, I'm having trouble solving a certain equation with given boundary conditions. I'm sure its probably something obvious that I'm overlooking but I was wondering if any of you would be kind enough to offer help. I tried using integration by parts but I think I'm still going wrong somewhere.

The initial equation is:
95635041tr3.gif

With boundary conditions of Vz=0 on r=R and Vz=V on r=kR

So I let
33202393fg9.gif


Then got
58058542yp8.gif


and used the BC's to give
19667250bz1.gif


I then tried to work out C to give
cequalsrz4.gif

(I think I might have started going wrong around here)

and inserted C into the above equations to give
94309658tr1.gif
.

I'm a bit stumped as to where I'm supposed to go from here. The solution is given with the question as being
19894834dk2.gif

Edit: The K in the solution is supposed to be small, not capital.

The only thing I can think of doing is dividing everything through by Vz to give V/Vz, which I can put on one side, but I'm pretty sure that's not what I'm supposed to be doing.

Thanks a lot to anyone who can offer advice.
 
Re: Solving eqn with given B.C's

aligee said:
Hi everyone, I'm having trouble solving a certain equation with given boundary conditions. I'm sure its probably something obvious that I'm overlooking but I was wondering if any of you would be kind enough to offer help. I tried using integration by parts but I think I'm still going wrong somewhere.

The initial equation is:
95635041tr3.gif

With boundary conditions of Vz=0 on r=R and Vz=V on r=kR

So I let
33202393fg9.gif


Then got
58058542yp8.gif


and used the BC's to give
19667250bz1.gif


You are replacing 'R' by "kR" - why?

Your b.c. is r = kR --- so replace
'r'

I then tried to work out C to give
cequalsrz4.gif

(I think I might have started going wrong around here)

and inserted C into the above equations to give
94309658tr1.gif
.

I'm a bit stumped as to where I'm supposed to go from here. The solution is given with the question as being
19894834dk2.gif

Edit: The K in the solution is supposed to be small, not capital.

The only thing I can think of doing is dividing everything through by Vz to give V/Vz, which I can put on one side, but I'm pretty sure that's not what I'm supposed to be doing.

Thanks a lot to anyone who can offer advice.
 
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