What is the direction of the magnetic field that produces the magnetic force on a negative charge as shown in each of the three cases in the figure below, assuming BB is perpendicular to vv?
Question by OpenStax is licensed under CC BY 4.0
Final Answer
  1. out of the page
  2. right
  3. into the page

Solution video

OpenStax College Physics for AP® Courses, Chapter 22, Problem 6 (Problems & Exercises)

OpenStax College Physics, Chapter 22, Problem 6 (PE) video thumbnail

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Video Transcript
This is College Physics Answers with Shaun Dychko. In this question, we have a negative charge that's moving in the direction shown by this green arrow and there's a force on it to the left in part (a) and so we have, with our right hand, our thumb directed to the top of the page because that's the direction of velocity, our palm is always in the direction of the force and so that's pointing to the left and our fingers are into the page but since this is a negative charge, we have to take the opposite answer to what the right hand rule says and so our fingers, which are the magnetic field direction, would be out of the page for a negative charge and so we are gonna draw circles with dots in them— these dots are like little arrowheads coming towards us— the magnetic field is out of the page here. In part (b), we have our thumb pointing down our palm is facing into the page because these are the tail feathers of an arrow going away from us so the force is into the page and our palm is in the direction of the force and this means our fingers are pointing to the left, which would be the answer if the moving charge was positive but since it's negative, we take the opposite to what the right hand rule says and so the magnetic field direction is to the right. Then for part (c), thumb to the left, palm facing up, fingers are out of the page but since it's a negative charge, we say into the page for the magnetic field direction so we have circles with x's.


These problems drive me nuts