A2L Item 199
- Description: Indicate the direction of the electric field at the origin due to two rods.
- Goal: Hone the concept of electric field
- Source: UMPERG-283-365
- Keywords: Distributed Charges, Electric Field, Electromagnetism
The question for students:
Two
uniformly charged rods are positioned horizontally as shown. The top
rod is positively charged and the bottom rod is negatively charged. The
total electric field at the origin
- is 0
- has both an x, and a y component
- points totally in the i direction
- points totally in the -i direction
- points totally in the j direction
- points totally in the -j direction
Commentary for teachers:
Answer
(6) By symmetry the field must point along the y-axis. Students who do not understand that the field points away from positive charges and towards negative charges would select #1 thinking that the fields cancel.