An electric heater element is made of Nichrome wire having resistivity equal to 100 ×10-8 ohm-metre. The diameter of the wire is 0.3 mm. Calculate the length of the wire required to get a resistance of 30 ohms.
As the heater element is Nichrome ρ = 100x 10-8 ?-m.
a = (π/4) (0.3×10-3 )2 m2
a = 7.069 x 10-8 m2
R =30 ?
R = ρ (I/a) or 30 = (100 ×10-8 × l)/ (7.069 ×10-8)
I = 2.12 m.