Question

The sides of a rectangular block are $2$cm, $4$cm and $6$cm. The ratio of maximum to minimum resistance between its parallel faces is?

• A. $4:1$
• B. $9:1$
• C. $1:2$
• D. $3:2$

Answer 1

The correct option is B $9:1$

The resistance of a conductor is
$R=\rho \frac{l}{A}=\rho \frac{l\cdot l}{Al}=\rho \frac{l^2}{V}$
Here, $V=$Volume of conductor $=$ constant
So, $R\propto l^2$
$\therefore \frac{R_{max}}{R_{min}}={\left(\frac{l_{max}}{l_{min}}\right)}^2$
$={\left(\frac{6}{2}\right)}^2$
$=\frac{9}{1}$.