A Zener diode of breakdown voltage \( 10 \, \text{V} \) is used as a voltage regulator as shown in the figure. The current through the Zener diode is:
\( 30 \, \text{mA} \)
\( 0 \)
\( 20 \, \text{mA} \)
\( 50 \, \text{mA} \)