What is the resistance of a conductor of unit length and unit cross-sectional area called?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Resistivity
For a conductor of length \( l \) and cross-sectional area \( A \), the resistance is \( R=\rho l/A \). Putting \( l=1 \) and \( A=1 \) leaves \( R=\rho \), so the resistance of a conductor of unit length and unit cross-sectional area is its resistivity.
NCERT (2026-27):
Ohm’s Law – “… and hence for a given conductor
\( \displaystyle R=\rho\,\frac{l}{A} \qquad (3.9) \)
where the constant of proportionality ρ depends on the material of the conductor but not on its dimensions. ρ is called resistivity.”