Parallel plates electric field · CAP 2006 #9
Physics · electromagnetism
Problem
One of two parallel metallic plates is uniformly charged with charge + q, and the other one is charged with charge -q. In this case, the electric field between them is E. When the negatively charged plate is discharged then recharged with a positive charge 4q, the electric field between the plates becomes: (a) 0; (b) 1.5 E; (c) 2.5 E; (d) 3E; (e) 5E.Intuitive explanation
The key is recognizing that the electric field between parallel plates depends on the difference in charge, not the individual charges. Initially, one plate has and the other , creating field . When you change the negative plate to , you're now dealing with charges and —so the net charge difference that drives the field has changed. Track how the field scales with this new charge configuration to find the new field strength.
Intuitive explanation
The key is recognizing that the electric field between parallel plates depends on the difference in charge, not the individual charges. Initially, one plate has and the other , creating field . When you change the negative plate to , you're now dealing with charges and —so the net charge difference that drives the field has changed. Track how the field scales with this new charge configuration to find the new field strength.