Page 397 - Physics Coursebook 2015 (A level)

Chapter 24: Capacitance
14
a Define the term capacitance of a capacitor. [2] b Figure 24.23 shows a circuit which can be used to measure the capacitance of a capacitor.
12 V
reed switch AB
67 mF
mA
Figure 24.23 For End-of-chapter Question 14.
The reed switch vibrates back and forth at a frequency of 50 Hz. Each time it makes contact with A the capacitor is charged by the battery so that there is a p.d. of 12 V across it. Each time it makes contact with B it is fully discharged through the resistor.
i Calculate the charge that is stored on the capacitor when there is a p.d. of 12 V across it. [2]
ii Calculate the average current in the resistor. [2]
iii Calculatetheaveragepowerdissipatedintheresistor. [3]
c A second capacitor of the same value is connected in series with the first capacitor.
Discuss the effect on both the current recorded and the power dissipated in the resistor. [4]
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