OpenStax College Physics for AP® Courses, Chapter 22, Problem 60 (Problems & Exercises)

This is College Physics Answers with Shaun Dychko. This picture gives us a wire, which in part (a) is a circle in the plane of this page and the magnetic field direction that a current in the wire produces. So we are gonna grab the wire with our right hand and point our fingers in the direction of the magnetic field, which is into the page inside the wire and observe which way our thumb is pointing on the wire. So if you grab the bottom of the wire here with your right hand with your fingers pointing into the page in the middle of the circle, your thumb is pointing to the left so this is the direction of the current and likewise, if you grab the wire up the top, you have to twist your right hand around to have your fingers pointing into the page in the middle and your thumb will be pointing to the right so this is right on the top of the loop so this would be described as clockwise... the current is clockwise. In part (b), your fingers should be going to the right inside this coil and if you grab this portion of wire at the front here then your thumb will be pointing downwards and the current is going like this and if you were to grab the wire that's on the other side of this coil with your fingers still pointing to the right because that's the direction of the magnetic field inside the coil, your thumb is pointing up and so the current is up in this portion, down in this portion and if you were to look at it from the left— so your observer is here— and looking at it from the left, this current would seem to be going clockwise... clockwise from the left. Okay! And then in part (c), with fingers pointing to the left because that's the direction of the magnetic field inside this coil, if you grab a portion of wire close to us then your thumb is pointing upwards and the portion of wire far from us we will need the thumb pointing down in order to have the fingers pointing to the left inside the coils and so this—if you were to look at it from the right—would be clockwise. So this is clockwise from the right or we could have said counter-clockwise from the left, depending on where you want to place your observer.