 Now we can look at question 4 on the backside and this is our calculation problem. So we've got the current in a circular loop of wire and it wants to know the magnetic field. So the special case equation for this that we saw earlier is this one here showing that the magnetic field is equal to mu naught i over 2r. My known values, again I can use the value for mu naught, our constant, our permeability of free space. It gives me the value for the current and it gives me the radius of the circular loop of wire. Now this just set a 0.2 meter circular loop but it is the radius that's being given there. Not the circumference around the loop or anything like that. Once I know those then I can go ahead and plug in my values and do my calculation. Again remember when you've got stuff on the bottom unlike I've got shown here you probably want to put an extra set of parentheses before you plug this into your calculator. So on your worksheet that you turn in make sure you give your final answer and make sure you took a look at all of these units to tell me what final unit you should have for the magnetic field.