Home - Education Resources - Science of NDT - Magnetism


After completing this section you will be able to do the following:

  • Explain how magnetic lines of force enter and exit a bar magnet.
  • Discuss how magnetic lines of force act upon other ferromagnetic objects.



  1. What happened when you placed the circular piece of metal in the magnetic lines of flux? Outside the lines?
  2. What do the lines around the bar magnet indicate?
  3. If the earth is like a huge magnet, with a magnetic pole at the north end and another magnetic pole at the south end, what might these imaginary lines look like around the earth?

What do the lines around the bar magnet indicate?

The lines that we have mapped out around the magnet, called the magnetic lines of force, indicate the region in which the force of the magnet can be detected. This region is called the magnetic field. If an iron object is near a magnet, but is not within the magnetic field, the object will not be attracted to the magnet. When the object enters the magnetic field, the force of the magnet acts, and the object is attracted. The pattern of these lines of force tells us something about the characteristics of the forces caused by the magnet. The magnetic lines of force, or flux, leave the north pole and enter the south pole.

How is the earth like a magnet?

Since the earth is a huge magnet with a magnetic north and south pole, the lines of magnetic force around the earth look like there is a huge vertical bar magnet running through the center of the earth. We will see in the next experiment how the magnetic lines of flux around a magnet can be seen. The next page will tell you more about how you can observe the magnetic field of a magnet and what you can learn from reading the patterns of the magnetic lines of force.