Question

If negligibly small current is passed though a wire of length 15 m & resistance of 5 $\Omega$, having uniform cross section of $6\times {10}^{-7}{m}^2$, then coefficient of resistivity of material is

• A. $1\times {10}^{-7}\Omega -m$
• B. $2\times {10}^{-7}\Omega -m$
• C. $3\times {10}^{-7}\Omega -m$
• D. $4\times {10}^{-7}\Omega -m$

Answer 1

The correct option is B $2\times {10}^{-7}\Omega -m$

We know that ,resistance $R=\frac{\rho L}{A}$

where $L=$length of wire, $\rho =$ coefficient of resistivity, $A=$ cross section.

Thus, $\rho =\frac{RA}{L}=\frac{5\times 6\times {10}^{-7}}{15}=2\times {10}^{-7}\Omega -m$