The size of a carbon block, having specific resistance. `3.5xx10^(-3)Omega-cm` is `2cmxx2cmxx2cm`. The resistance of the block between two square end faces and two opposite rectangular faces are respectively

Options

A. `17.5xx10^(-4)` and `1.75xx10^(-4)Omega`
B. `1.75xx10^(-4)` and `175xx10^(-4)Omega`
C. `175xx10^(-4)` and `1.75xx10^(-4)Omega`
D. `1.75xx10^(-4)` and `17.5xx 10^(-4)Omega`

Answer

C

Explanation

Specific resistance
`rho = 3.5xx10^(-3)Omega -cm`
`rho =R(A)/(l)rArr R = (rho l)/(A)`
Resistance R between square faces
`= (3.5xx10^(-3)xx20)/(4)=17.5xx10^(-3)=175xx10^(-4)Omega`
Resistance between opposite rectangular faces
`R = (3.5xx10^(-3)xx2)/(2xx20)=1.75xx10^(-4)Omega`