A zener diode of power rating \( 2 \, \text{W} \) is to be used as voltage regulator. If the zener diode has a breakdown of \( 10 \, \text{V} \) and it has to regular voltage fluctuated between \( 6 \, \text{V} \) and \( 14 \, \text{V} \), the value of \( R_{S} \) for safe operation should be _______ \( \Omega \).
