OpenStax College Physics for AP® Courses, Chapter 22, Problem 4 (Problems & Exercises)

This is College Physics Answers with Shaun Dychko. We are going to determine the direction of the velocity of a positive charge given the direction of the magnetic field and the direction of the force the charge experiences due to the magnetic field in each of these three scenarios. So we are going to use the right hand rule which says that we point our fingers in the direction of the magnetic field and you can remember that the fingers go in the direction of the magnetic field because there are many magnetic field lines and you have many fingers and so those are going to point out of the page with your right hand and the palm is going to be in the direction of the force and you can remember that because palms push things and exert forces on things— that's a way to remember that the palm is in the direction of the force so your palm is facing upwards— and when you have your hand arranged this way, your thumb is pointing to the left so the direction of the velocity of this charge is to the left. Now in part (b), we have our fingers pointing to the right and our palm is facing upwards and now our thumb is pointing straight out of the page and the thumb is the direction of the velocity of the positive charge and so we can draw a dot surrounded by a circle— this dot represents the point of an arrow coming out of the page towards us. And then in part (c), we have our fingers going in to the page because these are like tail feathers of an arrow going away from us so the magnetic field lines are in to the page. And we have our palm facing to the left because the palm is the direction of the force and our thumb is pointing upwards so the velocity is up in this part. There we go!