A parallel-plate capacitor with plate area and initial plate separation is connected…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A parallel-plate capacitor with plate area 5.0×10−2m2 and initial plate separation 1.0mm is connected to a 9.0V battery and allowed to reach steady state. While the battery remains connected, the plates are slowly pulled apart until the separation doubles.
Assume the dielectric between the plates is air (κ≈1) and that edge effects are negligible.
(a) Determine the charge on each plate after the separation has doubled.
(b) Calculate the work that must be done by an external agent to increase the plate separation from 1.0mm to 2.0mm while the battery remains connected.
(c) Explain the sign of the work computed in part (b) in terms of energy changes in the electrical system and the external agent.