19.1 Capacitors

Three capacitors, each of capacitance 27 μF, are connected as shown in Fig. 1.1.

Fig. 1.1

Calculate the total capacitance between points P and Q.

The maximum safe potential difference that can be applied across any one capacitor is 4 V. 

Determine the maximum safe potential difference that can be applied between points P and Q.

A capacitor consists of an insulator separating two metal plates, as shown in Fig. 1.3.

Fig. 1.3

The potential difference between the plates is V. The variation with V of the magnitude of the charge Q on one plate is shown in Fig. 1.4.

Fig 1.4

Explain why the capacitor stores energy but not charge.

Use Fig. 1.4 to determine: 

capacitance = ................................. μF [2]

energy = ................................. mJ [2]

State two functions of capacitors connected in electrical circuits.

Three capacitors are connected in parallel to a power supply as shown in Fig. 1.1. 

 

(ii)

Use your answer in (i) to show that the combined capacitance C_T of the three capacitors is given by the expression.

 

 

[2]

A student has available three capacitors, each of capacitance 24 μF. 

Draw circuit diagrams, one in each case, to show how the student connects the three capacitors to provide a combined capacitance of: 

[1]