# The Method of Images (Electromagnetism)

• I
• sinus
In summary, the method of images is a mathematical convenience to set a fixed potential to zero for a grounded conductor.

#### sinus

TL;DR Summary
What is the effect of the plane that being grounded make its electric potential become zero?
Can anyone explain to me why grounded means zero electric potential. I confuse what's the relation between infinite ground conducting plane and its electric potential (the method of images).

I have a several question:
1. Why the conductor plane must be infinite, while in reality there's no such one.
2. Why the electric potential must be zero to using this method?
2. If the plane isn't be grounded, does its electric potential not zero? What's exactly that making the potential in the plane zero when we grounded it? How ?
As far as I know that the electron easily run into the ground, does it mean the plane become positive charge?

It's arbitrary what you define to be zero because only potential differences matter. If there is a ground connection then that's usually defined to be zero.

There is too much context missing to answer your individual questions.
1. Conducting plates don't have to be infinite in general.
2. Which method?

sinus and Dale
sinus said:
1. Why the conductor plane must be infinite, while in reality there's no such one.
Because it makes the calculation easier. A large but finite plane would give approximately the same answer, but with more mathematical effort required.

sinus said:
2. Why the electric potential must be zero to using this method?
Because it makes the calculation easier. You can set it to any potential you like, but setting it to zero is convenient.

sinus said:
2. If the plane isn't be grounded, does its electric potential not zero?
Grounding allows the plane to accept charge without changing potential. So grounding produces a structure with a fixed potential. It is merely a mathematical convenience to set that fixed potential to zero.

sinus said:
What's exactly that making the potential in the plane zero when we grounded it? How ?
It is just an arbitrary choice. The value of potential is not physical. Only potential differences are physically meaningful.

sinus said:
As far as I know that the electron easily run into the ground, does it mean the plane become positive charge?
No. As I said above, grounding makes it so that the plane has a fixed potential which does not change as charges are added or removed.

sinus and hutchphd
mfb said:
It's arbitrary what you define to be zero because only potential differences matter. If there is a ground connection then that's usually defined to be zero.

There is too much context missing to answer your individual questions.
1. Conducting plates don't have to be infinite in general.
2. Which method?
Thank you for your reply sir, I finally understand the method of images. Sorry for long tome didn't respond. For your feedback,number 2: the method that I meant is the method of images, like why using that solutions method (thank god, now I know the reason)
For number 1, I don't follow. So for a finite conducting planes the method of images is still apply?

Dale said:
Because it makes the calculation easier. A large but finite plane would give approximately the same answer, but with more mathematical effort required.

Because it makes the calculation easier. You can set it to any potential you like, but setting it to zero is convenient.

Grounding allows the plane to accept charge without changing potential. So grounding produces a structure with a fixed potential. It is merely a mathematical convenience to set that fixed potential to zero.

It is just an arbitrary choice. The value of potential is not physical. Only potential differences are physically meaningful.

No. As I said above, grounding makes it so that the plane has a fixed potential which does not change as charges are added or removed.
Thank you so much for your explanation sir, it really helpful for me :)