Question

SI unit of resistivity is
A. Ohm metre
B. Ohmmeter $^{-1}$
C. Ohmmeter $^{-2}$
D. None of these

Answer 1

- Hint: Compute the mathematical expression for resistivity. Then find the SI unit of resistivity. You can find the derived units from seven fundamental units.

Complete step-by-step solution -
The International System of Units (SI) is the new type of the metric system. This system is official in the majority of the countries. It comprises of seven basic units of measurement as discussed below:
Metre (m)- It is used to measure length.
Seconds (s) – It is used to measure time.
Kilogram(kg)- It is used to measure mass.
Ampere (A)- It is used to measure electric current.
Kelvin (K) - It is used to measure temperature
Mole (mol)- It is used to measure the amount of substance.
Candela(cd)- It is used to measure luminous intensity.
Other units can be derived from these basic units.

Resistivity is the property that defines the resistance in a given material of length L. and area of cross-section A. Symbol of resistivity is $\rho $ Can be mathematically expressed as.
\[
\rho=R \times \dfrac{A}{l}
\]
Thus, its SI unit is ohmmeter.

Additional Information:
Conductors have low resistivity while insulators have high resistivity. For example, the resistivity of copper which is a good conductor is $1.72 \times 10^{-4}$ ohm-meter and resistivity of air which is a poor conductor is $1.5 \times 10^{14}$ ohm-meter.

Note: Other than the length and area of cross-section, resistivity also depends on nature and temperature of a conductor. Talking about other options, they are incorrect as there are no units like Ohmmeter $^{-1}$ and Ohmmeter $^{-2}$.