8 12 Analogue ammeters were used before digital meters became widely available. The analogue ammeter shown will measure a maximum current of 1.0 mA and has a resistance of 18 Ω. 0.4 0.6 0.8 1 0.2 0 (Source: © David J. Green/Alamy Stock Photo) The analogue ammeter can be adapted to measure a larger current by adding a resistor, known as a shunt, in parallel with the ammeter. The arrangement is shown below. The analogue ammeter is represented by the 18 Ω resistor. 2.0 A 18 Ω shunt The maximum current through the 18 Ω resistor remains as 1.0 mA. (a) Show that the shunt would need to have a resistance of about 0.01 Ω to adapt this ammeter to read up to a maximum current of 2.0 A. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. 9 Turn over (b) A shunt of this resistance was usually made from Manganin wire. Calculate the length of Manganin wire of radius 0.95 mm required to make this shunt. resistivity of Manganin = 4.55 × 10−7 Ω m (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Length = ...................................................... (Total for Question 12 = 6 marks)