1.1. The diagram below shows a circuit to charge a capacitor.

The electromotive force (e.m.f.) E of the cell is 1.48 V and it has negligible internal resistance. The resistance of the resistor is 120 kΩ and the capacitance of the capacitor is 2000 μF. At time t = 0 the capacitor is uncharged. The switch is closed at time t = 0.

Calculate the time t when the potential difference across the capacitor is 1.00 V.

t = ....................................................... s [4]

1.2. A capacitor of capacitance C is connected across a strip of conductive paper.

The switch is moved from X to Y, and the time t for the potential difference across the capacitor to halve is measured.

The time t is given by the expression

t = (Ck ln2) × L

where k is the resistance of the conductive paper per unit length and L is the length of the conductive paper.

The value of C is 1.2 × 10^–3 F.

In an experiment, L is changed and t measured.

The data points are plotted on a t against L grid as shown below.

Draw a straight line of best fit through the data points, and use the gradient of this line to determine k.

k = ............................................... Ω m^–1 [4]