Question

the resistiviy of micron wire 100micro ×ohm×cm . what length of wire of diameter 0.2mm is required to form a coil of resistance 20 ohm​

Answer 1

Given,

Resistivity = 100×10^-6 ohm/cm

Radius of wire = D/2 = 0.1mm = 10^-4m ;

Area of cross section = πr² = 3.14×10^-4×10^-4 = 3.14 × 10^-8 m².

Resistance = 20 ohm

Now,

R = ρl/A

l = RA/ρ

l = (20 × 3.14×10^-8)/100×10^-6

l = 0.00628m

l = 6.28 mm (Ans)