Consider a air-filled parallel-plate capacitor with plates of length 9.4 cm, width 6.13 cm, spaced a distance 1.77 cm apart. Now imagine that a dielectric slab with dielectric constant 2.8 is inserted a length 3.7 cm into the capacitor. The slab has the same width as the plates. The capacitor is completely filled with dielectric material down to a length of 3.7 cm.

A battery is connected to the plates so that they are at a constant potential 0.33 V while the dielectric is inserted. What is the ratio of the new potential energy to the potential energy before the insertion of the dielectric? Edge effects can be neglected.

From this, we can deduce that if a person inserts the slab part way into the conductor, and then releases it, the capacitor will exert a force on the dielectric in what direction?

1. pushing it out of the capacitor
2. toward the negatively charged plate
3. pulling it into the capacitor
4. there will be no force exerted on the slab
5. toward the positively charged plate