Question

A coil of copper wire has a resistance of 90ohm at 20°c and is conducted to a 230v supply. By how much should the voltage be increased to keep the current constant if the temperature of coil rises to 60°c

Answer 1

Take the temperature coefficient of resistance of copper as 0.00428 from 0°C.

$\frac{R_{60}}{R_{20}}= \frac{1+60×0.00428}{1+20×0.00428}$

$R_{60°C.} = 90 × \frac {1.2568}{1.0856 }= 104.2Ω$

$R_{20°C }= \frac{230}{90} = 2.56A$

Since the wire resistance has become 104.2Ω at 60°C

 $New voltage= 104.2 × 2.56= 266.3 V$

∴ increase in voltage required = 266.3 − 230 = 36.3 VR