The Zener diode has a $V_z=30 V$. The current passing through the diode for the following circuit is _________mA.

${\text{Current load resistance, I}}_L=\frac{V_Z}{R_L}=\frac{30}{5000}=6 mA$

${\text{Voltage drop across resistor in series, V}}_S=E-V_Z=90-30=60V$

${\text{Current through series resistance, I}}_S=\frac{V_S}{R_S}=\frac{60}{4000}=15 mA$

${\text{Thus, I}}_Z=I_S-I_L=15-6=9 mA$