Concepts Of Physics MCQ Edition [Volume 2]PhysicsCapacitors
A parallel-plate capacitor with a plate area of 400 cm ^2 and a separation of 1.0 mm is connected to a 100 V power supply. A 1.0 mm thick dielectric slab with a dielectric constant of 5.0 is inserted into the gap, and later, after disconnecting the power supply, the slab is removed. In both steps, the electrostatic energy increases. Which of the following best explains why the energy increases during both the inserti
Options
- ADuring insertion, the battery does work to supply additional charge; during removal, an external agent does wo
- BDuring insertion, the dielectric does work on the battery; during removal, the battery does work on the extern
- CDuring insertion, the capacitance decreases; during removal, the capacitance increases.
- DDuring insertion, charge is lost to the dielectric; during removal, charge is regained from the dielectric.
Correct answer
A. During insertion, the battery does work to supply additional charge; during removal, an external agent does wo
Step-by-step solution
When the dielectric slab is inserted with the battery connected, the capacitance increases. To maintain the constant voltage, the battery supplies additional charge, performing work. The work done by the battery ( W = Q V ) is twice the increase in the stored electrostatic energy, allowing the energy to increase while the slab is naturally pulled in. When the slab is removed with the battery disconnected, the charge on the plates remains constant. The induced bound charges on the dielectric surface are attracted to