1. The field coil of a motor has a resistance of 250Ω at 15°c.By how much will the resistance increase if the motor attained an average temperature of 45°c when running?Take the temperature coefficient as 0.00428/°c referred to 0°c.
2. A copper rod,0.4m long and 4.0mm in diameter has a resistance of 5500.02μΩm at 20°c.Calculate the resistivity of copper at that temperature. If the rod is drawn out into a wire having a uniform diameter of 0.8mm,calculate the resistance of the wire when its temperature is 60°c.Assume the resistivity to be unchanged and the temperature coefficient of resistance of copper to be 0.00426/°C at 0°C.
