This is College Physics Answers with Shaun Dychko. We'll use the Right Hand Rule to figure out the direction of the magnetic field. Our thumb is going to point upwards, in the direction of the current which is the conventional current and that is the direction of flow of positive charge. So the thumb of our right hand is pointing up, our palm is facing to the left because that's the direction of the force, and our many fingers are pointing in the direction of the many magnetic field lines and that is into the page. And so the magnetic field is going into the page. These exes represent the tail feathers and arrow moving away from us into the page. In part b, we have our thumb pointing down and our palm is facing into the page because this force is going into the page. And our fingers end up pointing to the left. So the magnetic field lines are to the left in part b. And then for part c, we have our thumb pointing to the left, our palm facing to the top of the page and our fingers are pointing out of the page. And so we draw dots which are like the arrow tips of an arrow coming towards you. And there we go.
What is the direction of the magnetic field that produces the magnetic force shown on the currents in each of the three cases in Figure 22.55, assuming $B$ is perpendicular to $I$?