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.
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.
The maximum current through the 18 Ω resistor remains as 1.0 mA.
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.
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
Length = ......................................................
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