A capacitor consists of two parallel metal plates, separated by air, at a variable distance x apart, as shown in [Figure 6.1]. The capacitance C is inversely proportional to x. The capacitor is charged by a supply so that there is a potential difference (p.d.) V between the plates. State expressions, in terms of C and V, for the charge Q on one of the plates and for the energy E stored in the capacitor.

1. (a)A capacitor consists of two parallel metal plates, separated by air, at a variable distance x apart, as shown in [Figure 6.1]. The capacitance C is inversely proportional to x. The capacitor is charged by a supply so that there is a potential difference (p.d.) V between the plates. State expressions, in terms of C and V, for the charge Q on one of the plates and for the energy E stored in the capacitor.[1]
2. (b)(i)The charged capacitor in (a) is now disconnected from the supply. The plates of the capacitor are initially separated by distance L. They are then moved closer together by a distance D, as shown in [Figure 6.2]. State expressions, in terms of C, V, L and D, for: the new capacitance C_N[1]
3. (b)(ii)the new charge Q_N on one of the plates[1]
4. (b)(iii)the new p.d. V_N between the plates.[1]
5. (c)Explain whether reducing the separation of the plates in (b) results in an increase or decrease in the energy stored in the capacitor.[1]

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