The problem statement, all variables and given/known data Two point charges a and b whose magnitudes are same positioned at a certain distance along the positive x axis from each other. a is at the origin. The graph is drawn between electrical field strength and distance x from a. E is taken positive if it is along the line joining from a to b. From the graph it can be decided that 1) a is +ve b is -ve 2) a and b are both +ve 3) a and b are both -ve 4) a is -ve and b is +ve The attempt at a solution As the electric field is defined with respect to a positive unit charge, a should be postive. This is because the field strength near a is tending to postive infinity, and according to the question, this is from a to b. So, this can be interpreted as repulsion. As we move towards the middle of the graph, the strength decreases, almost to zero, so the field from point charge b must be cancelling it out. So b is also positive. But why does the graph go towards positive infinity again? Because if b is also postive, won't it push our test postive unit charge away? This direction would be from b to a, right? Shouldn't the graph go to negative in that case? The answer is given as a and b both being positive. Thanks for helping!