The parallel-plate capacitor used on each key of a computer keypad is a square 0.7 cm on a side. Between the plates is a dielectric with k = 4.4. When the key is in the "up" position, the plate separation is 0.76 mm.
A. Find the initial capacitance.
B. How far must the key be depressed for a keystroke to be registered, which happens when the capacitance increases by 3.9 pF (pico Farads)?