# Adding a "sheet charge" to a volume charge distribution
**URL:** https://community.freefem.org/t/adding-a-sheet-charge-to-a-volume-charge-distribution/2401
**Category:** General Discussion
**Created:** [April 17, 2023, 8:55pm UTC](https://community.freefem.org/t/adding-a-sheet-charge-to-a-volume-charge-distribution/2401 "2023-04-17T20:55:11Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@marchywka](https://community.freefem.org/u/marchywka)
#### Post date: [April 17, 2023, 8:55pm UTC](https://community.freefem.org/t/adding-a-sheet-charge-to-a-volume-charge-distribution/2401/1 "2023-04-17T20:55:11Z")
I could post some code but thought it may be less confusing to just describe
the objective and see if anyone can point to a specific example that
may be useful. I am doing an “electropolishing” exercise where I have
1 electrode in a conducting fluid with the rough surface etching
as the simulation progresses. Some early normalized tests were really
cool so I thought I would try to clean them up with more accurate expression.
I’m using a “phase field” to describe the solid and wanted to put a sheet of
charge at a specific location. The levelset and isoline functions appear to work
very well and I can create an expression for the required charge based on
the potential gradient. However, I think I need something like the
element thickness, h normal to the line, to get the quantity right. I found things
like hTriangle and lenedge but not sure what to use to turn the
sheet charge into a volume. Any thoughts or examples?
In actuality it is a 2D mesh so I guess these are areal and line charges.
Thanks.
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### Author:  [@marchywka](https://community.freefem.org/u/marchywka)
#### Post date: [April 19, 2023, 4:32pm UTC](https://community.freefem.org/t/adding-a-sheet-charge-to-a-volume-charge-distribution/2401/2 "2023-04-19T16:32:37Z")
fwiw, it looks like lenEdge/area works although I have not
checked it in a lot of controlled conditions 🙂