What is the electrical resistivity of a material? What is its $SI$ unit? Describe an experiment to study the factors on which the resistance of a conducting wire depends.

(N/A) Electrical resistivity is defined as the resistance offered by a material of unit length and unit cross-sectional area. Mathematically,$R = \rho (l/A)$,where $\rho$ is the resistivity. Its $SI$ unit is ohm-metre $(\Omega \, m)$. To study the factors affecting resistance: $1$. Take a battery,an ammeter,a plug key,and nichrome wires of different lengths but same thickness. $2$. Connect the wire in the circuit and measure the current using the ammeter. $3$. Observe that resistance increases with the length of the wire $(R \propto l)$. $4$. Repeat the experiment using wires of the same length but different cross-sectional areas. $5$. Observe that resistance decreases as the area of cross-section increases $(R \propto 1/A)$.