Also, $R = \rho \frac{l}{A}$ $ \Rightarrow $ $\frac{{{R_1}}}{{{R_2}}} = \frac{{{l_1}}}{{{l_2}}} \times \frac{{{A_2}}}{{{A_1}}} = {\left( {\frac{{{A_2}}}{{{A_1}}}} \right)^2}{\left( {\frac{{{d_2}}}{{{d_1}}}} \right)^4}$
$ \Rightarrow $ $\frac{{24}}{{{R_2}}} = {\left( {\frac{d}{{d/2}}} \right)^4} = 16$ $ \Rightarrow $ ${R_2} = 1.5\,\Omega $.



