Question

Dimensions of a block are $1\,cm × 1\,cm × 100\,cm$. If specific resistance of its material is $3\times 10^{-7} \,\Omega\, m$, then the resistance between the opposite rectangular faces is

• A. $3\times 10^{-7} \,\Omega\, m$
• B. $3\times 10^{-9} \,\Omega\, m$,
• C. $3\times 10^{-5} \,\Omega\, m$,
• D. $3\times 10^{-3} \,\Omega\, m$,

Answer 1

Answer: (A)

Here length $l=1\,cm=10^{-2}\,m$

Area of cross-section, $A = 1\,cm\times100\,cm$
$= 100 \,cm^{2}$
$=10^{-2}\,m^{2}$
Resistance, $R=\rho \frac{\ell}{A}=3\times10^{-7}\times\frac{10^{-2}}{10^{-2}}$
$=3\times10^{-7}\,\Omega$