the field resistance of a dc machine is 50 ohm at

Question

The field resistance of a dc machine is 50 ohm at 20^oC. The resistance increases to 55 ohm at 50^oC. Find the temperature coefficient of the resistance material.

Ans:

Solution:

R = R_o[1 + α(t-t_o) where R and R_o are resistances at 50^oC and 20^oC

50 x 30 x α = 5

α = 5/1500= 3.3 x 10^-3/^oC