A parallel plate capacitor with air between its plates is charged to 86.6 V and then disconnected from the battery. When an unknown dielectric material is placed between the plates, the voltage across the capacitor drops to 21.519 V. What is the dielectric constant of the unknown material? Assume that the material fills the space between the plates completely.

A parallel plate capacitor with air between its plates is charged to 86.6 V and then disconnected from the battery. When an unknown dielectric material is placed between the plates, the voltage across the capacitor drops to 21.519 V. What is the dielectric constant of the unknown material? Assume that the material fills the space between the plates completely.