Carbon, silicon, and germanium have four valence electrons each. These are characterized by valence and conduction bands separated by the energy bandgap respectively equal to \((E_g)_C, (E_g)_{Si}~\text{and}~(E_g)_{Ge}\). Which of the following statements is true?

1.	\((E_g)_{Si} < (E_g)_{Ge}<(E_g)_{C}\)
2.	\((E_g)_{C} < (E_g)_{Ge}>(E_g)_{Si}\)
3.	\((E_g)_{C} > (E_g)_{Si}>(E_g)_{Ge}\)
4.	\((E_g)_{C} =(E_g)_{Si}=(E_g)_{Ge}\)

In an unbiased \(\mathrm{p\text-n}\) junction, holes diffuse from the \(\mathrm{p\text-}\)region to the  \(\mathrm{n\text-}\)region because:

For a transistor amplifier, the voltage gain:

In a half-wave rectification, what is the output frequency if the input frequency is \(50~\text{Hz}?\)
1. \(50~\text{Hz}\)
2. \(100~\text{Hz}\)
3. \(25~\text{Hz}\)
4. \(60~\text{Hz}\)

For a CE-transistor amplifier, the audio signal voltage across the collector resistance of \(2\) k\(\Omega\) is \(2\) V. Suppose the current amplification factor of the transistor is \(100.\) What is the base current if the base resistance is \(1\)  k\(\Omega?\)
1. \(14\) \(\mu\)A
2.  \(12\) \(\mu\)A
3.  \(15\) \(\mu\)A
4.   \(10\) \(\mu\)A

Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of \(10\) and the second has a voltage gain of \(20.\) If the input signal is \(0.01\) volt, the output ac signal is:
1. \(1.0\) V
2. \(2.4\) V
3. \(2\) V
4. \(1.5\) V

A \(\text{p-n}\) photodiode is fabricated from a semiconductor with a bandgap of \(2.8~\text{eV}.\) The energy of the incident photon with a wavelength of \(6000~\text{nm}\) is:
1. \(0.207~\text{eV}\)
2. \(0.270~\text{eV}\)
3. \(0.027~\text{eV}\)
4. \(0.072~\text{eV}\)

The number of silicon atoms per \(\text m^3\) is  \(5 × 10^{28}.\) This is doped simultaneously with \(5 × 10^{22}\) atoms per \(\text m^3\) of Arsenic and \(5 × 10^{20}\) per \(\text m^3\) atoms of Indium. The number of holes is:
(given that \(n_{i} = 1 . 5 \times 10^{16} ~\text m^{- 3}\))
1. \(4.51\times 10^{9}\)
2. \(4.99\times 10^{22}\)
3. \(1.56\times 10^{22}\)
4. \(3.33\times 10^{23}\)

In an intrinsic semiconductor, the energy gap \(E_g\) is \(1.2~\text{eV}.\) Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at \(600~\text{K}\) and that at \(300~\text{K}?\) 
(assume that the temperature dependence of intrinsic carrier concentration \(n_{i}\) is given by; \(n_{i} = n_{0} \exp \left[\frac{- E_{g}}{2 k_{B} T}\right],\) where \(n_0\) is the constant)
1. \(1.01\times10^6:1\)
2. \(1.09\times10^5:1\)
3. \(1:1\)
4. \(1:2\)