Question
What is the direction of the magnetic field that produces the magnetic force on a positive charge as shown in each of the three cases in the figure below, assuming BB is perpendicular to vv?
<b>Figure 22.52</b> Find the magnetic field direction given the force and velocity of a positive charge shown.
Figure 22.52 Find the magnetic field direction given the force and velocity of a positive charge shown.
Question by OpenStax is licensed under CC BY 4.0
Final Answer
  1. into the page
  2. left
  3. out of the page

Solution video

OpenStax College Physics, Chapter 22, Problem 5 (Problems & Exercises)

OpenStax College Physics, Chapter 22, Problem 5 (PE) video thumbnail

In order to watch this solution you need to have a subscription.

Start free trial Log in
vote with a rating of votes with an average rating of .
Video Transcript
This is College Physics Answers with Shaun Dychko. We're going to use the Right Hand Rule to determine the direction of the magnetic field lines in each of these three scenarios. Now, this I represents the direction of conventional current which is the movement of positive charges. And so we can directly use the Right Hand Rule to figure out which way the magnetic field lines must be pointing. So our thumb point in the direction of velocity of positive charges and so that's going to be straight up. Our palm faces the direction of the force. And our fingers are you can think of are mini fingers that are going to be aligned in the direction of the mini field lines of magnetic field. And that is into the page. And so we can draw exes here to represent magnetic field into the page. In part b, we have our thumb pointing down. Our palm is in the direction of the force which is into the page because this x represents an arrow going away from you because you just see the tail feathers of the arrow moving away from you into the page. And so our palm is facing flat against the page, thumb is down and our fingers of our right hand are pointing to the left. And so we draw an arrow to the left, that's the direction of magnetic field. If you're not getting the same answers, make sure you're using your right hand because it's a common mistake in the use of the left hand. So, in part c, we have our thumb pointing to the left, our palm is facing upwards and our fingers are pointing out of the page. And so we draw dots to represent an arrow head coming towards you. This magnetic field line is coming out of the page.

Comments

What would happen if the charge was negative?

It would just be the opposite of what it is for a positive charge using right-hand rule, or you can use left-hand rule for negative charge.