The truth table for the given logic circuit is

In the circuit diagram shown in figure, the current through the zener diode is

The depletion layer in p-n junction region is caused by

The collector supply voltage is 6 V and a voltage drop across a resistor of $600 \Omega$ in the collector circuit is 0.6 V , in a circuit of transistor connected in common emitter mode. If the current gain is 20 then the base current is