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
Verified Correct Answer: B.
Physical Principles & Numerical Solution
R = PL/A => L = RA/P = 21 x 4π x 108/1.1 x 10-6 = 2.40
Source: Myschool Past Questions Archive (Record #24285)