Recent content by sweep123

aha. I get it, Thanks a lot that's brilliant. Don't think I would have ever got that on my own:smile:

Not sure if your allowed to bump threads on this forum...o:)

Okay so Jfree=J. also D=εE so E=D/ε and therefore J=σD/ε edit: so ∇ · σD/ε = −∂(ρfree)/∂t or (∇σ/ε)· D + (σ/ε)(ρfree) = −∂(ρfree)/∂t Doesn't feel like I am getting anyhere

I could sub the first eq into the second to get the divergence of current density equals the negative differential of the divergence of the electric displacement field, or ∇ · Jfree = −∂(∇ · D)/∂t Can Jfree and total J be considered to be the same thing in this example? Also I will lose ρ...

Homework Statement Show that any charge distribution in a conductor of conductivity σ and relative permittivity κ vanishes in time as ρ = ρ0exp(−t/ζ) where ζ = κǫ0 σ Homework Equations Maxwell's equation ∇ · D = ρfree equation of continuity for a free charge density ∇ · Jfree =...

oh yeah. i should have spent a bit more time on that. Thanks

ive just tried substituting the particular integral y(x)= c1(x^2)sin(x)+c2(x^2)cos(x)+xc3sin(x)+xc4cos(x) into y"+y=xsinx. I end up with 2c1sin(x)+4xc1cos(x)+2c2cos(x)-4xc2sin(x)+2c3cos(x)-2c4sin(x)=xsin(x) This doesn't look solvable. I've checked my differentiating a couple of times and...

thanks. that's really helpful. is there anyway of knowing what the particular integral is for any unhomogenous second order differential equation, or is it just trial and error?

Homework Statement solve y"+y=xsin(x) , initial conditions y(0)=0, y'(0)=1 Homework Equations The Attempt at a Solution I know that when right hand side equals something like sin(x), then the particular integral is xc1sin(x)+xc2cos(x). I am unsure what the particular integral...

I understand that people are only helping voluntarily. It is just a bit frustrating watching new topics popping up at the top which get replies very quickly and then watching my topic move further and further down the page.

I did all the things on the FAQ and yet still no one has viewed my question about the wave equation. Why is this?

[SOLVED] Satisfying wave equation Homework Statement Confirm that the following wave satisfies the wave equation and obtain an expression for the velocity of a wave Y=Asin(2x-5t)*e^(-2t) Homework Equations the wave equation is (d^2y/dt^2)=(V^2)*(d^2y/dx^2) The Attempt at a...

Does anyone know the interplanar spacing of the crystals NaCl and KCl. Thanks

1. Homework Statement A wedge with mass M rests on a frictionless horizontal table top. A block with mass "m" is placed on the wedge. There is no friction between the block and the wedge. The system is released from rest. A. Calculate the acceleration of the wedge. B. Calculate the...