A Zener diode, having breakdown voltage equal to 10 V, is used in voltage regulator circuit shown in figure.  The current through the diode is

Voltage across zener diode and load resistance remains same.

$Current through load resis\tan ce : I_L=\frac{V_0}{R_L}=\frac{10}{2\times {10}^3}=5mA$

$Voltage across series resis\tan ce :\hspace{0.17em}{V}_S = V-V_Z=25-10 = 15\hspace{0.17em}V$

$Current through series resis\tan ce : I_s=\frac{V_s}{R_S}=\frac{15}{500}=0.03A=30mA$

$$\begin{gathered} So, \\ Current through diode : I_Z=I_S-I_L=30-5=25mA \end{gathered}$$