Drawing Magnetic Fields

This activity covers magnetic fields and also serves as an introduction to vector fields, which are a common theme through most electrical engineering disciplines. As discussed in the lesson closure, understanding the Earth's magnetic field is important in designing ways of protecting astronauts in space. Students play the role of engineers when they apply their understanding of magnets to design devices to solve the problem presented in the grand challenge later in the unit.

After this activity, students should be able to:

• Explain the significance of the directions of magnetic field lines.
• Draw the shape of magnetic field lines around a permanent magnet.

An understanding of what types of materials are affected by magnetic fields and that compasses point to Earth's magnetic poles.

(Hold up a compass.) We know that this compass points to the magnetic north pole of the earth—which also happens to be the geographic north, roughly. It does that because it is also a magnet and opposite poles of magnets attract. That means this compass will also point along the magnetic field that any nearby magnet creates, not just the earth's. We are going to track a whole lot of points around your magnet to see what its magnetic field looks like.

Set-up

• Make copies of the Permanent Magnetic Field Worksheet (PDF), one per student.
• Have ready the required materials for each group.

With the Students

1. Divide the class into groups of two students each. Hand out the worksheets.
2. On the worksheet, have students mark 30 points uniformly around the magnet, making sure the points are adequately spread out across the paper and are about 1 in to 3 cm apart.
3. Students place the magnet on the paper so that the poles are facing left and right on the paper. Note that ceramagnets have wide, flat poles so the magnets will be balanced upright on their edges.
4. Students place the compass centered over one point and allow the needle to settle.
5. Whichever way the north or red end of the needle points, they are to mark an arrow on that point.
6. Students repeat 5 and 6 until all points have been marked with an arrow for the magnetic field direction.
7. Have several representative examples drawn on the board by students of their magnetic fields. Question the whole class as to their agreement or disagreement with the field lines. Identify any disagreements or problems. Make sure to drive home to students that the field lines always loop away from north and back to south.

Worksheets: Review students' completed worksheets to assess their depth of comprehension. Assessments are conducted in accompanying lessons 3 and 4 when students use this information as engineers would to design solutions to the grand challenge for the unit.

The ceramagnets must be balanced upright and on their edges. If enough are available, it is helpful to use two magnets together as they balance easier and should fit into the rectangle drawn on the sheet. If the magnets are lying flat on the paper, the field will be moving into and out of the paper, which the compass cannot track when laid flat on the paper.

Because the ceramagnets are not marked with definite poles, students must leave the magnet in place on the paper throughout the tracing. If the magnet's orientation is flipped, the compass needle will point the opposite way, creating an incoherent overall field drawing.

It is possible, especially through the multiple uses of the compasses, for their polarity to be reversed. This should not present a problem provided the magnet is not moved and students are consistent in which direction of the needle they used to mark the arrow.