A2L Item 246
- Description: Identify the electrical quantities that change when a conducting cylinder is removed from between the plates of a capacitor.
- Goal: reason and link electrical quantities
- Source: 283-Del C, E, U, etc. - cstV
- Keywords: Electromagnetism, Reasoning, Capacitors
The question for students:
Two
parallel conducting plates form a capacitor. With a metal cylinder of
length half the plate separation inserted between the plates, it is
connected to a battery with potential ΔV. The cylinder is now removed.
Which of the quantities C, ΔV, Q, E, and U change?
- C, E, and U only
- Q and U only
- C and U only
- E and U only
- Q, ΔV, and U only
- ΔV and E only
- C and Q only
- None of the above
Commentary for teachers:
Answer
(8) Since ΔV does not change, E must because the distance between plates doubles. If E changes, so must Q. If Q changes, so must C. Finally, that U chages can be seen in a variety of ways.
There are many good follow up questions, such as: How would the quantities change if the cylinder was made of a dielectric material?