Question

A manganin swamp resistance is connected in series with a moving coil ammeter consisting of a milli-ammeter and suitable shunt in order to

• A. minimise the effect of temperature variation
  
• B. obtain large deflecting torque
• C. reduce the size of the meter
• D. minimize the effect of stray magnetic fields

Answer 1

The correct option is A minimise the effect of temperature variation

• Coil is made of copper.

A swamping resistance$\left(R_{sw}\right)$ of manganin (which has a negligible temperature coefficient) having a resistance 20 to 30 times the coil resistance is connected in series with the coil and a shunt of manganin is connected across this combination .

• Since copper forms a small fraction of the series combination, the proportion in which the currents would divide between the meter and the shunt would not change appreciable with the change in temperature.