The energy band diagrams for semiconductor samples of silicon are as shown. We can assert that:

 

1.	Sample \(X\) is undoped while samples \(Y\) and \(Z\) have been doped with a third group and a fifth group impurity respectively.
2.	Sample \(X\) is undoped while both samples \(Y\) and \(Z\) have been doped with a fifth group impurity.
3.	Sample \(X\) has been doped with equal amounts of third and fifth group impurities while samples \(Y\) and \(Z\) are undoped.
4.	Sample \(X\) is undoped while samples \(Y\) and \(Z\) have been doped with a fifth group and a third group impurity respectively.

An LED is constructed from a \(\mathrm{p\text{-}n}\) junction diode using \(\mathrm{GaAsP}.\) The energy gap is \(1.9~\text{eV}.\) The wavelength of the light emitted will be equal to:
1. \(10.4 \times 10^{-26}~ \text{m}\)
2. \(654~ \text{nm}\)
3. \(654~ \text{m}\)
4. \(654\times 10^{-11}~\text{m}\)

In an NPN transistor amplifier, if 98% of electrons emitted from the emitter reach the collector, then the value of collector current for the base current of 40 $\mu$A will be:

1. 1.96 mA             

2. 1.92 mA             

3. 1.96 A             

4. 1.92 A

In a common emitter amplifier, the phase difference between input signal and output signal is:

1. zero             

2. $\mathrm{\pi }$               

3. $\frac{\mathrm{\pi }}{2}$               

4. $\frac{\mathrm{\pi }}{4}$

If the reverse bias in a junction diode is changed from \(5~\text V\) to \(15~\text V\) then the value of current changes from \(38~\mu \text{A}\) to \(88~\mu \text{A}.\) The resistance of the junction diode will be:
1. \(4\times10^{5}\) 
2. \(3\times10^{5}\)
3. \(2\times10^{5}\)
4. \(10^{6}\)

In a common emitter circuit, if V_CC is changed by 0.2 V, collector current changes by 4 x 10^–3 mA. The output resistance will be:

1. 10 k$\mathrm{\Omega }$ 

2. 30 k$\mathrm{\Omega }$ 

3. 50 k$\mathrm{\Omega }$ 

4. 70 k$\mathrm{\Omega }$

When a transistor is used as a switch, it is in:

1.  active state.

2.  cut-off state.

3.  saturation state.

4.  both cut-off and saturation states are possible.

Use of transistor as an amplifier works in the:

1.  Cut off region

2.  Saturation region

3.  Passive region

4.  Active region