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]
- 0.42m
-
2.40 m
- 6.25 m
- 183.75 m
- 590.00 m
The correct answer is: B
Explanation
R = PL/A => L =
RAP
= 21 x 4π x 1081.1 x 10-6
= 2.40