In an unbiased p-n junction, holes diffuse from the p-region to n-region because :

1.	free electrons in the n-region attract them.
2.	they move across the junction by the potential difference.
3.	hole concentration in p-region is more as compared to n-region.
4.	All the above.

When a forward bias is applied to a p-n junction, it

1. raises the potential barrier.
2. reduces the majority carrier current to zero.
3. lowers the potential barrier.
4. None of the above.

For a transistor amplifier, the voltage gain:

In a half-wave rectification, what is the output frequency if the input frequency is \(50\) 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 p-n photodiode is fabricated from a semiconductor with a bandgap of \(2.8\) eV. The energy of the incident photon with a wavelength of \(6000\) nm is:
1. \(0.207\) eV
2. \(0.270\) eV
3. \(0.027\) eV
4. \(0.072\) eV

The number of silicon atoms per m³ is 5 × 10²⁸. This is doped simultaneously with 5 × 10²² atoms per m³ of Arsenic and 5 × 10²⁰ per m³ atoms of Indium. The number of holes is: (Given that $n_i=1.5\times {10}^{16} m^{-3}$)

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 Eg is 1.2eV. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at 600K and that at 300K? Assume that the temperature dependence of intrinsic carrier concentration $n_i$ is given by, 

${\mathrm{n}}_{\mathrm{i}}={\mathrm{n}}_0\exp \left[\frac{-{\mathrm{E}}_{\mathrm{g}}}{2{\mathrm{K}}_{\mathrm{B}}\mathrm{T}}\right] \mathrm{where} {\mathrm{n}}_0 \mathrm{is} \mathrm{a} \mathrm{constant}.$

1. \(1.01\times10^6:1\)
2. \(1.09\times10^5:1\)
3. \(1:1\)
4. \(1:2\)

Which statement is true for the given circuit:

1. (a) is OR gate and (b) is NOT gate.
2. (a) is NOT gate and (b) is OR gate.
3. (a) is AND gate and (b) is OR gate.
4. (a) is OR gate and (b) is AND gate.