A2L Item 227
- Description: Identify the motion of a charge released from rest in external E and B fields.
- Goal: Reason regarding electrodynamics
- Source: 283-630 Path of a charge in E&B fields.
- Keywords: Electric Field, Electromagnetism, Forces, Magnetic Field, Right-Hand Rule
The question for students:
A
charge is released from rest in E and B fields. Both fields point along
the x axis. Which of the following statements regarding the charge’s
motion are correct?
- The charge will travel along a straight-line path.
- The charge’s speed will change as it travels.
- The charge will travel in helical path.
- The charge will travel in helical path of increasing pitch.
- The charge will travel in a circle in the x-y plane.
- 1 and 2 only
- 2 and 4 only
- None of the above
Commentary for teachers:
Answer
(6) The different responses reveal the extent to which students understand vector cross products and/or read the problem carefully. Some students choose #8 because they do not like the way the motion is expressed. They prefer descriptions such as, the charge first moves in a straight line until it gets some speed then …