I’m confused about this problem with the right hand rule. example

According the book: My thumb should point up (as expected)

My fingers should point into the page (I don’t know how that would work)

My palm should be facing the left.

I’m not sure how that’s supposed to work. Normally when doing the right hand rule, I would align my fingers and thumb in the direction of the vectors, then the direction of my palm would tell me which way the vector would point into or out of the page but this is a little different

  • $\begingroup$ From your description, this seems to correspond to your usual way of using the right hand rule. You point your thumb up — in the direction of the velocity $\mathbf{v}$ — and your fingers away from you/into the page — in the direction of the magnetic field $\mathbf{B}$. Then your palm is facing left, which is the direction of the force $\mathbf{F}$. What's the confusion? $\endgroup$
    – d_b
    Feb 15 at 23:45
  • $\begingroup$ I’m confused about fingers pointing into the page. From my experience with the right hand rule, the thumb and finger point in the 2D direction and the palm points into or out of the page. $\endgroup$
    – Ibby
    Feb 15 at 23:55
  • $\begingroup$ That's because you are learning, and your experience with the right hand rule is limited. Here is a new situation in which you can apply the right hand rule. It's slightly different from what you have seen before, but it's nonetheless a valid application of the RHR. $\endgroup$
    – d_b
    Feb 15 at 23:59
  • $\begingroup$ I get that but how do fingers point into the page? The only way I could see that happening is if my palm is facing down not left. I think if I saw a picture or something it would be clear but it’s hard to explain my confusion with text since I’m having a visual issue $\endgroup$
    – Ibby
    Feb 16 at 0:16
  • $\begingroup$ If your right hand palm is facing down, your extended thumb is pointing to the left which is the wrong direction; your thumb should point in the direction of $\vec v$: upwards. $\endgroup$
    – John Darby
    Feb 16 at 0:36

From your comment, it seems like a simple photograph would help clear things up, so here is one. My thumb points up, my fingers point into the page (or screen, in this case), and my palm faces left.

enter image description here

  • $\begingroup$ Yes. That’s perfect. Thank you for clarifying $\endgroup$
    – Ibby
    Feb 16 at 0:30
  • $\begingroup$ Resourceful. +1 $\endgroup$
    – Gilbert
    Feb 16 at 1:38

I suspect your issue is with how to interpret the image on the paper. So there are three vectors of interest when a charged particle is moving through a magnetic field and they are as follows.

  1. The field lines: This is where your fingers should be pointing. The 'X'es in the image means that they are pointing into the paper.

  2. The motion of the particle: This is where your thumb should be pointing. Up on the paper as indicated by the arrow.

  3. The force on the particle: This is the force exerted on the particle by the magnetic field and conveniently in the direction your palm is pointed assuming you aligned your hand correctly with the previous 2 vectors.

If you think about this as a continuous motion it quickly becomes clear that the particle will trace a circle in a counter clockwise direction. If you ever come across a negatively charged particle moving through a magnetic field you can just go ahead and use your left hand instead.


$\vec F = q(\vec V \times \vec B)$ is the applicable relationship, and here $q$ is positive (proton). If the thumb, the forefinger, and the middle finger of the right hand are bent at right angles to one another with the thumb pointed in the direction of motion of the proton relative to a magnetic field and the forefinger in the direction of the field, then the middle finger will point in the direction of the induced electromotive force. As stated the problem uses your palm instead of your middle finger (see picture in answer by @d_b).


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