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 ...

Answer Details

The resistance of a wire is given by the formula: R = (ρ * L)/A Where R is resistance, ρ is resistivity, L is the length of the wire and A is the cross-sectional area of the wire. To find the length of the constantan wire required to construct a standard resistor of resistance 21Ω, we rearrange the formula to get: L = (RA)/ρ Substituting the given values, we have: L = (21 * 4π x 10^-8)/ (1.1 x 10^-6) L = 0.76 meters Since the value of π was given as 22/7, we use the approximate value of π = 3.14 in the calculation. Therefore, the length of the constantan wire required to construct a standard resistor of resistance 21 Ω is 0.76 meters. So, the correct option is (b) 2.40 m.