A2L Item 179

Goal: Recognizing the properties of magnetic fields

Source: 283 – field of wire

Oersted discovered that there is a magnetic field in the space
around wires carrying currents. Consider a long thin straight wire with
a current I. Which of the following statements about the magnetic field
lines is true?

  1. Field lines are parallel to the
  2. Field lines are perpendicular to the wire.
  3. Field
    lines are directed radially away from the wire.
  4. Field lines are
    circles centered on any point on the wire.
  1. A only
  2. B only
  3. C only
  4. D only
  5. A and C only
  6. B and D only
  7. B and C only
  8. None of them is true.



(6) It is important to elicit reasons that students selected any
of the other responses. Rather than telling the correct answer have
students draw the field lines. Often they are able to reproduce pictures
they have seen but cannot describe the fields in words.