A2L Item 201
- Description: Indicate the configurations of uniformly charged rods for which the electric field at the origin is along the x-axis.
- Goal: Reason regarding electric fields
- Source: 283-10, E at origin due to charged rods
- Keywords: Distributed Charges, Electric Field, Electromagnetism, Vectors
The question for students:
All of the configurations shown below consist of charged rods of the
same length L. The magnitude of the total charge is also the same for
each rod. The total charge in each rod is distributed uniformly.<div
class="img-center">
</div>For which
configuration(s) is the electric field vector at the origin in the
positive x direction?
- 2 only
- 1 and 3 only
- 5 only
- 4 only
- 1 and 5 only
- None of the above
Commentary for teachers:
Answer
(4) Because they are given lots of examples involving point charges, spheres and rings, students often miss the fact that there are many situations for which the direction of the field can be deduced even though determining the value or formal expression for the field is way beyond them.