Figure 8 When the switch S is in position 1 , the capacitor is connected to a 12.0 V supply and the ammeter shows the current that is charging the capacitor. To discharge the capacitor, the switch is moved to position 2 .
21 Capacitance Exam-style questions OCR Physics A © Oxford University Press 2016 This resource sheet may have been changed from the original 6 The magnitude of the current through the ammeter A during the charge or discharge period is shown in Figure 9. Figure 9 a A student makes the following two statements about the charging and discharging processes. 1 The variation of the magnitude of the current with time, as shown in Figure 9, is the same in each case. 2 The needle on the centre-zero ammeter is in a different position in each case. Explain why both of these statements are correct. ( 2 marks ) b Use data from Figure 9 to show that the value of the resistor R is 20 k . ( 2 marks ) c i The time constant for the circuit is 5.0 s. By sketching suitable lines on Figure 9, explain how this may be determined from the graph. ( 2 marks ) ii Show that the capacitor C has a capacitance of 250 μF. ( 2 marks )