Figure shown a DC voltage regulator circuit, with a Zener diode of breakdown voltage =6V. If the unregulated input voltage varies between 10V to 16V, then what is the maximum Zener current?

Correct option is B. 3.5mA
Maximum current will flow from zener if input voltage is maximum.
When zener diode works in breakdown state, voltage across the zener will remain same.
∴Voltage across 4kΩ = 6V
∴Current through 4kΩ = 6/4000 A = 1.5 mA
Since input voltage = 16V
∴Potential difference across 2kΩ = 10V
∴Current through 2kΩ = 10/2000 A = 5 mA
∴Current through zener diode = (IS - IL) = 5 mA - 1.5 mA = 3.5 mA