A moving-coil instrument, which gives full-scale deflection with 15 mA, has a copper coil having a resistance of 1.5 at 15 C, and a

A moving-coil instrument, which gives full-scale deflection with 15 mA, has a copper coil having a resistance of 1.5 Ω at 15 °C, and a temperature coefficient of 1/234.5 at 0 °C, in series with a swamp resistor of 3.5 Ω having a negligible temperature coefficient.
Determine: 

(a) the resistance of shunt required for a full-scale deflection of 20 A;

(b) the resistance required for a full-scale deflection of 250 V. If the instrument reads correctly at 15 °C, determine the percentage error in each case when the temperature is 25 °C.