Potential at a point multiple choice question ( aqa)

[bonbon22]

Homework Statement:

https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2018/june/AQA-74082-QP-JUN18.PDF
question 22 on the multiple choice near the end

Relevant Equations:

no equations

I understand how they arrived at the answer of 2Q , but i have a couple of questions on this. If one of the charges were negative for example how would the resultant potential be found then? at the middle point would i add the positive charges and subtracted the negative ? Also what would the potential be at for the corner , for example the bottom left corner assuming the charges were Q, Q, Q , 2Q?

 

[Doc Al]

If one of the charges were negative for example how would the resultant potential be found then?

What's the potential from a point charge? How does it depend on the sign of the charge? (Note: Potentials from multiple charges can just be added like scalars.)

 

[bonbon22]

What's the potential from a point charge? How does it depend on the sign of the charge? (Note: Potentials from multiple charges can just be added like scalars.)

makes sense. what would the poential be at the bottom left corner?

 

[Doc Al]

makes sense. what would the poential be at the bottom left corner?

You tell me. If you know the charges and their distance from the bottom left corner, you can find the potential at that point from those charges. (Don't include the potential from the charge residing there, since the problem becomes unphysical at zero distance.)