Electric Potential - Conceptual question

[EngineerHead]

Homework Statement

At a certain distance from a point charge, the magnitude of the electric field is 500 V/m and the electric potential is -3.00 kV. (a) What is the distance to the charge? (b) What is the magnitude of the charge?

Homework Equations

The Attempt at a Solution

a) 6 meters
b) -2 micro-Coulombs
*These are correct, I mention this fact cause I don't want you to have to waste your time checking so.

My question is: for part b, if you solve for Q, the magnitude of charge, from E instead of V (E = kq/r^2), what is the visual concept behind why the charge is negative? Because obviously if you solve from V, you will get a negative 2 uC.

Of course the book asks for magnitude anyway, but the answer key gives the negative sign as well. I want to understand the concept behind it.

 

[Doc Al]

My question is: for part b, if you solve for Q, the magnitude of charge, from E instead of V (E = kq/r^2), what is the visual concept behind why the charge is negative?

You cannot tell the sign of Q just using E, since you were not told the direction of the field.

 

[EngineerHead]

Thank you, and just to verify - because of the potential given, it is a fact that the charge is negative?

 

[Doc Al]

Thank you, and just to verify - because of the potential given, it is a fact that the charge is negative?

Yes.