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]
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]
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