- #1
ylem
- 32
- 1
Hello!
Just hoping for a bit of help on a homework problem I'm doing at the moment...
Basically this is the question:
Three point charges are placed along the y axis: a charge q at y=a, a charge -2q at the origin and a charge q at q=-a. Such an arrangement is called an electric quadrupole.
a. Find the magnitude and direction of the electric quadrupole at points along the positive x-axis.
b. Use the binomial expansion to find an approximate expression for the electric field valid for x>>a. Contrast this behaviour to that of the electric field of a dipole.
I've tried to do this loads of different ways...
I've basically used E = 1/4pi...q/r^2 (didn't know how do get a symbol for the permittivity of free space!) and then for the vector have put (xi - aj) for q at a and so on... But then when I add them up to come up with a total E I just get something that looks really messy - although it is to the power of a half and could be expanded using the binomial, it just looks wrong...
Any input on how I could try to solve the question would be greatly appreciated!
Thanks, Sam(antha)
Just hoping for a bit of help on a homework problem I'm doing at the moment...
Basically this is the question:
Three point charges are placed along the y axis: a charge q at y=a, a charge -2q at the origin and a charge q at q=-a. Such an arrangement is called an electric quadrupole.
a. Find the magnitude and direction of the electric quadrupole at points along the positive x-axis.
b. Use the binomial expansion to find an approximate expression for the electric field valid for x>>a. Contrast this behaviour to that of the electric field of a dipole.
I've tried to do this loads of different ways...
I've basically used E = 1/4pi...q/r^2 (didn't know how do get a symbol for the permittivity of free space!) and then for the vector have put (xi - aj) for q at a and so on... But then when I add them up to come up with a total E I just get something that looks really messy - although it is to the power of a half and could be expanded using the binomial, it just looks wrong...
Any input on how I could try to solve the question would be greatly appreciated!
Thanks, Sam(antha)