A Zener diode with a breakdown voltage of 6 V is connected in a voltage regulator circuit. If the supply voltage is 10 V and the series resistor is 200 Ω, what is the current through the series resistor?

The voltage across the series resistor is $V_R = V_{supply} - V_Z = 10 - 6 = 4$ V. The current through the series resistor is $I = V_R / R = 4 / 200 = 0.02$ A $= 20$ mA. This is the total current supplied to both the Zener and any load connected in parallel.