(i) In n-type semiconductor, the semiconductor is doped with pentavalent impurity. The electrons are majority carriers and holes are minority carriers or n_e >> n_h , (n_e = number density of electrons, n_h = number density of holes).
In energy band diagram of n-type semiconductor, the donor energy level E_D is slightly below the bottom of conduction band E_c and thus. the electron can move to conduction band, even with small supply of energy.
  
(ii) In p-type semiconductor, the semiconductor is doped with trivalent impurity. The holes are the majority carriers and electrons are the minority carriers, i.e. n_b >> n_e . In energy band diagram of p-type, the acceptor energy level E_A is slightly above the top of valence band E_V .
Thus, even with small supply of energy, electron from valence band can jump to level E₄ and ionise the acceptor, negatively.

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

\(\beta =I_{ c }/I_{ b }=10^{ -3 } \ / \ (20\times 10^{ -6 })=50 \ ;\)
Voltage gain, \(A_{ V }=\beta \frac { R_{ C } }{ R_{ i } } =50\times \frac { 4000 }{ 1000 } =200\)

Here,\(E=1.14 \ eV=1.14\times 1.6\times 10^{ -19 } \ J\)
\(\\ \lambda =\frac { hc }{ E } =\frac { 6.62\times 10^{ -34 }\times 3\times 10^{ 8 } }{ 1.6\times 10^{ -19 }\times 1.14 } =10,888 \ A°\)

The mobility of electrons in \(n\)-type semiconductor is more than the mobility of holes in \(p\)-type semiconductor. Since the \(n\)-type semiconductor has electrons as majority carriers and holes as minority carriers, whereas the \(p\)-type semiconductor has holes as majority carriers and electrons as minority carriers, therefore mobility of  \(n\)-type is more than that of  \(p\)-type.

Note that thermally generated electrons (ni ~10¹⁶m^–3) are negligibly small as compared to those produced by doping.
Therefore, ne \(\approx\) ND
Since n_e n_h = \(n_{i}^{2}\) , The number of holes
n_h = (2.25 x 10³² ) / (5 x10²²)
= ~ 4.5 x 10⁹ m^–3

\(75 \ ; \ 1000 \ \Omega \ ; \ .075 \ S, \ 450\)
\(\Delta V_{ i }=20\times 10^{ -3 }V \ ; \ \Delta I_{ b }=20\times 10^{ -6 }A \ ;\)
\( \Delta I_{ C }=1.5\times 10^{ -3 }A \ ;\ R_{ 0 }=6\times 1000\Omega .\)
\( \beta _{ a.c. }=\frac { \Delta I_{ C } }{ \Delta I_{ b } } =\frac { 1.5\times 10^{ -3 } }{ 20\times 10^{ -6 } } =75\)
\(R_{ i }=\frac { \Delta V_{ i } }{ \Delta I_{ b } } =\frac { 20\times 10^{ -3 } }{ 20\times 10^{ -6 } } =1000\Omega \)
Transconductance \(=\frac { \Delta V_{ i } }{ \Delta I_{ b } } =\frac { 1.5\times 10^{ -3 } }{ 20\times 10^{ -6 } } =0.075\quad S\)
Voltage gain \(=\beta _{ a.c. }\times R_{ 0 }/R_{ i }\)
\( =75\times 6000/1000=450\)

(i) 3 (ii) 180 (iii) 10800 (iv) 1.8 V
(i) Resistance gain  \(=\frac { R_{ 0 } }{ R_{ i } } =\frac { 6 }{ 2 } =3\)
(ii) Voltage gain, \(A_{ V }=\beta \frac { R_{ 0 } }{ R_{ i } } =60\times 3=180\)
(iii) Power gain \(=\beta ^{ 2 }\frac { R_{ 0 } }{ R_{ i } } =(60)^{ 2 }\times 3=10800\)
(iv) Output voltage \(=A_{ V }\times input\ voltage\)
\(=180\times (10\times 10^{ -3 })=1.8V\)

(i) Solar panel is a panel having large number of solar cells fitted side by side on it.
(ii) Solar cell is basically a solar energy concerter.It is a \(p-n\)junction device which converts solar energy into electrical energy .If this energy is stored in a capacitor,it can be used for glowing bulbs.
 (iii) Manoj displayed his will to do something for society.Trough his shear in a capacitor,it can be used for glowing bulbs.
(iii) Manoj displayed his will to do something  for soceity.Through his shear efforts,he got electricity within the reach of villagers, who were suffering otherwise.?The work of Manoj was highly appreciated by villagers.

(i) The most important use of zener diode is in marking the constant voltage power supply.
(ii) The essential conditions for proper working of Zener diode are as follows:
(a) The Zener diode must be reverse biased
(b) The Zener diode must have voltage greater than Zener break down voltage.
(c) The Zener diode is to be used in a circuit  where current is less than the maximum Zener current limited by the power rating of the given Zener diode.
(iii) To be happy in life,one has to be like a Zener diode which evens out all fluctuations and displays a constant output. Ups and downs are part of life.One who evens them out is successful and happy.