A 6 V / 2.5 mA relay is connected in the output stage of a transistor. The coil is made of aluminium having α = 0.004. The resistance of the coil is 600 ? at 32o C. Calculate the resistance of the coil at 42o C.
Ans:
α = 0.004
R (at 320C) = 600 ?
T = 273 + 32 =305
R = R0 (1+ α T)
600 = R0 (1+ 0.004 x 350) = 2.4 R0
R0 = 600/2.4 =250 ?
R (at 420C)
T = 273 + 42 = 315
R = R0 (1+ α T) = 250 (1 + 0.004 x 315) R = 565 ?