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(a) Sketch the electric field lines near a point charge $+q$. (b) Do the same for a point charge $-3.00q$.

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Solution Video

# OpenStax College Physics for AP® Courses Solution, Chapter 18, Problem 47 (Problems & Exercises) (1:06)

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Video Transcript
This is College Physics Answers with Shaun Dychko. A positive charge q will have electric field lines radiating outwards from it because these electric field lines point in the direction that there would be a force on a positive test charts placed here. So for positive test charge that placed here, we repelled from this charge plus q and so electric field line is pointing in that direction, away from the charge. Then in part b, we have negative three q, so a positive test charge placed here would experience a force towards this charge of negative three q. And so the electric field lines have to point towards it. And electric field lines are going to be more dense because this charge has a magnitude three times greater than the charge in part a. And so, I've drawn three times of many field lines. So, in part a there are one, two, three, four, five, six lines radiating outwards. And in part b, if you count them all up there are 18 lines here pointing inwards.