A capacitor consists of two rectangular metal plates 3 meters by 4 meters, placed a distance 2.5 mm apart in air (Figure
20.86). The capacitor is connected to a 9-volt battery long enough to charge the capacitor fully, and then the battery is
removed.
(a) Prove that there will not be a spark in the air between the plates.
(b) How much charge is on the positive plate of the capacitor?
With the battery still disconnected, you insert a slab of plastic 3 meters by 4 meters by 1 mm between the plates,
next to the positive plate, as shown in Figure 20.86. This plastic has a dielectric constant of 5.
(c) After inserting the plastic, you connect a voltmeter to the capacitor. What is the initial reading of the voltmeter?
(d) The voltmeter has a resistance of 100 megohms (1 × 108 ohms). What does the voltmeter read 3 seconds after being
connected?