Hi and point charge vector question

[Jim Newt]

Hi all this is my first post. This looks like a great forum and hopefully I can contribute in some way to the discussion. I have a question about JPEG I attached; hopefully you all can see it.

What is the strategy for "reducing the charges"? For instance, why is -3q reduced to -2q and -2q reduced to -q etc.? Any advice would be helpful. Thanks,

Jim

 

[Doc Al]

Looks to me that someone wanted to create a new problem (with different charges) without redoing the diagram. They just crossed out the old charges and wrote in the new charges. The fields from the three non-zero charges are labeled E1, E2, & E3.

 

[awvvu]

I think they simplified the problem by removing some charges, which cancel out to 0. It just makes it easier to compute.

 

[Jim Newt]

Thanks for the input. Like awvvu said, it was just a simplification of the problem that made it easier to solve.