A2L Item 228
- Description: Identify the motion of a charge with initial velocity in external E and B fields.
- Goal: Reason regarding electrodynamics
- Source: 283-635 Path of a charge in E&B fields.
- Keywords: Electric Field, Electromagnetism, Forces, Magnetic Field, Right-Hand Rule
The question for students:
A
charge has an initial velocity parallel to the y-axis 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 a helical path.
- The charge will travel in a 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
(7) A common response is #4 because they forget that increasing pitch implies that the speed changes.