Pure Si at 500 K has equal number of electron $\left(n_{\mathit{e}}\right)$ and hole $\left(n_{\mathit{h}}\right)$ concentration of $1.5\times {10}^{\mathrm{16 }}{\mathrm{m}}^{-3}.$ Doping by indium increases $n_{\mathit{h}}$ to $4.5\times {10}^{22}$ ${\mathrm{m}}^{-3}.$ The doped semiconductor is of:

1.	n-type with electron concentration \(n_{e}=5\times10^{22}~m^{-3}\)
2.	p-type with electron concentration \(n_{e}=2.5\times10^{23}~m^{-3}\)
3.	n-type with electron concentration \(n_{e}=2.5\times10^{10}~m^{-3}\)
4.	p-type with electron concentration \(n_{e}=5\times10^{9}~m^{-3}\)

A Zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit, as shown in the figure. The current through the diode is:

1. 10 mA

2. 15 mA

3. 20 mA

4. 5 mA

In a PN-junction diode:

The electrical circuit used to get smooth output from a rectifier circuit is called:

1. oscillator.

2. filter.

3. amplifier.

4. logic gates.

Two PN-junctions can be connected in series by three different methods as shown in the figure. If the potential difference in the junctions is the same, then the correct connections will be:

The correct symbol for zener diode is:

1.		2.
3.		4.

Which of the following logic gate is a universal gate?

1. OR                       

2. NOT

3. AND                     

4. NOR

How much is the forbidden gap (approximately) in the energy bands of germanium at room temperature? 
1. \(1.1~\text{eV}\)
2. \(0.1~\text{eV}\)
3. \(0.67~\text{eV}\)
4. \(6.7~\text{eV}\)

In a good conductor, the energy gap between the conduction band and the valence band is
1. Infinite
2. Wide
3. Narrow
4. Zero

A Ge specimen is doped with Al. The concentration of acceptor atoms is $~{10}^{21}$ $\mathrm{atoms}/{\mathrm{m}}^3$. Given that the intrinsic concentration of electron hole pairs is $~{10}^{19}/{\mathrm{m}}^3$, the concentration of electrons in the specimen is: