Give, power = 1 W, Zener breakdown, V_Z = 5 V
Minimum voltage, V_min = 3 V
Maximum voltage, V_max = 7 V
Current, \({ I }_{ Zmax }=\frac { P }{ { V }_{ Z } } =\frac { 1 }{ 5 } =0.2A\)
The values of R_S for safe operation,
\({ R }_{ S }=\frac { { V }_{ max }-{ V }_{ Z } }{ { I }_{ Zmax } } =\frac { 7-5 }{ 0.2 } =\frac { 2 }{ 0.2 } =10\Omega\)

The circuit resembles AND gate. The BOOLEAN expression of this circuit is, V₀ = A.B i.e. V₀ equals A AND B. The truth table of this gate is as given below:

Consider the circuit in figure given below to find the change in reading. As we know that, the formula for base current,\({ I }_{ B }=\frac { { V }_{ BB }-{ V }_{ BE } }{ { R }_{ 1 } } \) 

As R₁ is increased, I_B is decreased.
Now, the current in ammeter is collector current I_C.
I_C = \(\beta\)I_B, as I_B is decreased, I_C also gets decreased and the reading of voltmeter and ammeter are also decreased.

If emitter is reverse biased and collector is forward biased, then emitter works as collector and collector is work as emitter. In such situation, transistor works but has lower amplification because the size of  emitter is smaller than collector and doping of emitter is more than collector.

In elemental semiconductor,the band gap is such that the emissions are in infrared and not in visible region.