Calculate the length of a constantan wire of cross- sectional area 4 π x 10-8m2 and resistivity 1.1 x 10-6 Ω m required to construct a standard resistor of resistance 21 Ω. [Take π = 22/7]

Calculate the length of a constantan wire of cross- sectional area 4 π x 10-8m2 and resistivity 1.1 x 10-6 Ω m required to construct a standard resistor of resistance 21 Ω. [Take π = 22/7]

Calculate the length of a constantan wire of cross- sectional area 4 π x 10^-8m² and resistivity 1.1 x 10^-6 Ω m required to construct a standard resistor of resistance 21 Ω. [Take π = 22/7]

A 0.42m
B 2.40 m
C 6.25 m
D 183.75 m
E 590.00 m

waec 1992 physics

The correct answer is B. 2.40 m

R = PL/A => L = RA/P = 21 x 4Ï x 10⁸/1.1 x 10^-6 = 2.40

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