A constantan wire of length 50 cm and 0.4 mm diameter is used in making a resistor. If the resistivity of constantan is 5 × 10-7 m, calculate the value of the resistor.

Answer:- l = 50 cm = 0.5 m, d = 0.4 mm = 0.4 × 10-3 m, r = 0.2 × 10-3 m, p = 5 × 10-7 Ωm To Find: Value of resistor (R) Formula: ρ = RAl

Now,

Area A=πr2

A=π (0.2×10−3)2 m2

R=Aρl​=π×0.2×0.2×10−65×10−7×0.5​

R=1.99 Ω

Calculation: from formula, ∴ R = 1.989