A heater element is made of nichrome wire having resistivity equal to 100 × 10-8 ohm-m. The diameter of the wire is 0.4mm. Calculate the length of the wire required to get a resistance of 40 ?.
Ans:
When the heater element is Nichrome ρ = 100x 10-8 ?-m.
a = (π/4) (0.4 x10-3)2 m2
a = 12.6 x 10-3 m2
R = 40?
R = ρ (l/a) = 40 = (100 x 10-8 x l)/(12.6 x 10-3)
l = 5 m.