# Image charge method to find Green's function

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1. Oct 23, 2014

hi guys,
my professor told me in the class that when we would like to determine green function there are two general method i.e using image charge and using orthonormal eigen function. However I don't understand what are the specific differences between them. Anybody can help me? Moreover in the problem systems that solved by using image charge (as far as I have seen), there is always point charge there. Can image charge method be used in a problem like finding green function in a space (without charge) between 2 infinite parallel conducting plates for example?

2. Oct 23, 2014

### HallsofIvy

Can you give an example of finding Green's function by either method?

3. Oct 23, 2014

That's why I am asking, can we use both of them for same problem or not ?

4. Oct 23, 2014

### clem

The Green's function is defined as the potential due to a point charge with all surfaces grounded.
The image charge method is difficult to use for 2 parallel plates, because that requires an infinite set of image charges.

5. Oct 23, 2014

### elsafo

Oh unfortunately I have a task to solve it usi b g image charge

6. Oct 24, 2014

### vanhees71

The only difference between the two methods is that the image-charge method is not always applicable in practice. Of course, at the end you get the same result with both methods when applicable. It works for the half-plane and the sphere straight-forwardly. For two parallel plates I think you can use it, introducing an infinite series of image charges and summing up their contributions.

Since this is a typical home-work problem, you should ask this question in the homework section.