Question

Two circular electrodes with a diameter of 5.0 mm and a 0.10 mm-thick sheet of Mylar between them are attached to a 9.0 V battery. The battery is disconnected and then the Mylar is withdrawn. (Very small spacers keep the electrode separation unchanged.)

K = 3.1 for Mylar.

Does the energy stored in the capacitor increase, decrease, or stay the same when the mylar is removed? Briefly explain your reasoning.

Do not calculate the change in energy, just explain in terms of concepts related to capacitance (for example, charge, voltage, electric field).

Answer 1

The energy stored in the capacitor will decrease when the Mylar is removed because Mylar's dielectric properties allow more energy to be stored, and its removal lowers the capacitance.

Step-by-step explanation:

When the Mylar is removed from between the two circular electrodes of a charged capacitor, the energy stored in the capacitor will decrease. This happens because Mylar has a dielectric constant (K) of 3.1, which increases the capacitor's capacitance and allows more energy to be stored for the same voltage. Once the Mylar (dielectric) is removed, the capacitance decreases to its original value (the value it has in the air or vacuum), and so does the energy stored. Since the battery is disconnected and the charge remains constant, the energy, which is a function of both charge and voltage (Energy = 1/2 CV2), decreases as the capacitance C decreases.