Zener Diode

The $6 \mathrm{V}$ Zener diode shown in the figure has negligible resistance and a knee current of $5 \mathrm{mA}$. The minimum value of $\mathrm{R}\mathrm{ }\left(\mathrm{in}\mathrm{ }\mathrm{\Omega }\right)$ so that the voltage across it does not fall below $6 \mathrm{V}$ is