29.5 Magnetic Dipoles
We were able to calculate the on-axis magnetic field of a current loop, but determining the field at off-axis points requires either numerical integrations or an experimental mapping of the field. FIGURE 29.19 shows the full magnetic field of a current loop. This is a field with rotational symmetry, so to picture the full three-dimensional field, imagine Figure 29.19a rotated about the axis of the loop. Figure 29.19b shows the magnetic field in the plane of the loop as seen from the right. There is a clear sense, seen in the photo of Figure 29.19c, that the magnetic field leaves the loop on one side, “flows” around the outside, then returns to the loop.
FIGURE 29.19 The magnetic field of a current loop.
There are two versions of the right-hand rule that you can use to determine which way a loop’s field points. Try these in Figure 29.19. Being able to quickly ascertain the field direction of a current loop is an important skill.
TACTICS BOX 29.2 Finding the magnetic field direction of a current loop
Use either of the following methods to find the magnetic field direction:
1 Point your right thumb in the direction of the current at any point on the loop and let your fingers curl through the center of the loop. Your fingers are then pointing in the direction in which leaves the loop.
2 Curl the fingers of your right hand around the loop in the direction of the current. Your thumb is then pointing in the direction in which leaves the loop.
Workbook Exercises 18–20