3. A 4700 HF capacitor is discharged through a 2200 $2 resistor. To the nearest second, how long will it take for the charge on the capacitor to fall to half its original value? A. 3s B. 5s C. 7s D. 10s 4. The circuit shown in Fig. 12.1 is used to determine the capacitance of a capacitor. R 6.0V C A Fig. 12.1 The switch S is closed at time t = 0 s. This allows the 6.0 V battery to charge the capacitor C. The switch is then opened at time t= 20 s, allowing the capacitor to discharge through resistor R. The graph of Fig. 12.2 shows how the current I in the ammeter varies with time. 3.0 1/mA 2.5 2.0 1.5 1.0 0.5 0.0 0 10 20 30 40 50 60 70 80 90 100 t/ seconds Fig. 12.2 15Use the data to show that R has a value of about 2 kQ 11 . calculate a value C for the capacitance of C