Question

Which is the expression for resistivity of a wire of length $l$ and cross-section area A?

• A. $\rho =\frac{Rl}{A}$
• B. $\rho =\frac{RA}{l}$
• C. $\rho =\frac{A}{Rl}$
• D. $\rho =\frac{RA}{l^2}$

Answer 1

Answer: (B)

$\rho =\frac{RA}{l}$

Resistance R of a conductor depends on the length l and area of cross section A of the conductor Where, (rho) is called resistivity of the conductor it is also called as specific resistance. If we put $l=1m$ and$A=1sq.m$. then we get, $R=\rho$. Therefore, $R=\rho \frac{L}{A}$.
Thus, resistivity of a conductor is defined as the resistance of a conductor of unit length and unit area of cross section. The SI unit of resistivity is ohm metre. Resistivity is the characteristic property of material. It is different for different materials.