Question

The resistivity of a given wire of cross sectional area 0.7mm^2 is 4.9×10^-4mm. Calculate the resistance of a 2m lenght of the wire.

Answer 1

The resistance $R$ and resistivity $\rho$ of the wire are connected with the following relation:

$$R = \rho\dfrac{L}{A}$$

where $L = 2m$ is the lenght of the wire and $A = 0.7mm^2 = 0.7\cdot 10^{-6}m^2$ is the cross sectional area of the wire.

Substituting the numerical values, get:

$$R = 4.9\cdot 10^{-7}\Omega\cdot m\cdot \dfrac{2m}{0.7\cdot 10^{-6}m^2} = 1.4\Omega$$

Answer. R = 1.4 Ohms.