
$\frac{X}{R}=\frac{l_{1}}{100-l_{1}}$
$X=R\left(\frac{l_{1}}{100-l_{1}}\right)$
$12=18\left(\frac{l_{1}}{100-l_{1}}\right)$
$1200=30 l_{1}$
$l_{1}=40 \mathrm{cm}$
When $R=8$ ohm,
$12=8\left(\frac{l_{2}}{100-l_{2}}\right)$
$1200=20 l_{2}$
$l_{2}=60 \mathrm{cm}$
Hence, distance through $J$ is shifted is
$l=l_{2}-l_{1}=20 \mathrm{cm}$





Figure:
| Column $- I$ | Column $- II$ |
| $(A)$ Drift Velocity | $(P)$ $\frac{m}{n e^{2} \rho}$ |
| $(B)$ Electrical Resistivity | $(Q)$ $\mathrm{ne} v_{\mathrm{d}}$ |
| $(C)$ Relaxation Period | $(R)$ $\frac{\mathrm{eE}}{\mathrm{m}} \tau$ |
| $(D)$ Current Density | $(S)$ $\frac{E}{J}$ |
