 Being able to find the direction of the magnetic field is important. It will determine how things will behave inside this field. So let's run through a few examples, finding the direction of the magnetic field around a current. Let's say this is a current carrying wire, and in it, there is a current going up. Now, how do you find the magnetic field towards the left of the wire? Well, we'll use the right-hand ball. Point your thumb in the direction of the current, and then curl your fingers around the wire. Now, to the left of the wire, my finger should point towards you, which means that the magnetic field towards the left of the wire points out of the screen and towards you. This time, I have a current going towards you, and I want to find the magnetic field below the wire. So I point my thumb in the direction of the current, curl my fingers around, and below the wire, my fingers are pointing towards the right, which means that the magnetic field below the wire points towards the right. So what if I was told there is a clockwise magnetic field around this current? Well, I'll curl my fingers around clockwise, and my thumb should indicate the direction of the current. So in this case, my thumb points towards me, which tells me that the current generating a clockwise magnetic field points into the screen towards me. Now, knowing how to find the magnetic field is good and all, but we need to be able to read and express magnetic fields on paper. You can't meet and talk to everyone face to face after all, and this is what you'll be examined on. So let's look at a few examples on paper. So in this case, we have a current going towards the right, and we want to find the direction of the magnetic field at the dot. So applying the right hand rule and putting our thumb in the direction of the current, our fingers curl around and they point out of the screen towards us. To indicate a magnetic field coming out of the screen, we use a dot. In the second example, we have a current going down, again looking at the direction of the magnetic field at the point, and using the right hand rule, we have the magnetic field going into the screen at that point. We use across the show the magnetic field going into the screen. In this case, we have a current going into the screen. So point our thumb into the screen and then curl our fingers around. Where the dot is, your finger should point down, and so the direction of the magnetic field at this point is down. And in the last example, we have a current coming out of the screen. So I'm pointing a thumb out of the screen and curling our fingers around. Where the point is, your finger should point down and towards the right. So the direction of the magnetic field at this point is down and to the right. And if we wanted to show the entire magnetic field, we just draw the field lines. For a current going towards the right, it would have a circular magnetic field. On top of the wire, the magnetic field would point out of the screen towards us, and below the wire, the magnetic field would point into the screen, away from us. And because the magnetic field looks like this across the entire length of the wire, we would draw this across the entire wire. The magnetic field is stronger closer to the current, and so the field lines closer to the current are also denser. So further away from the current, you would have sparser field lines. In this case, we have the current going down. The magnetic field would go into the screen on the left-hand side of the current, and would come out of the screen on the right-hand side of the current. So we'd do the same thing as before, using dots to represent out of the screen and crosses to represent into the screen, and density of field lines is same as before as well. If we have a current going into the screen, then we would have a circular magnetic field around that current, and it would point in the direction that our fingers curl. So in this case, it's clockwise. And the magnetic field doesn't just exist on one ring around the current. It exists all around the current, so we have multiple field lines. The last example is very similar to the previous one, except this time we have the current pointing out of the screen instead of into the screen. And so the magnetic field would point anti-clockwise.