(i) It is used for personal communication and cellular phones offer voice and data connectivity with high speed.
(ii) Transmission of news across the globe is done within a few seconds.
(iii) Using Internet of Things (UIT), it is made possible to control various devices from a single device. Example: home automation using a mobile phone.
(iv) It enables smart classrooms, online availability of notes, monitoring student activities etc. in the field of education.

V_BE =0.7V
Input junction is a forward biased.
Since,
V_BE = 0.7V
V_CE = V_BE+ V_CB
V_CB = V_CE-V_BE
To determine V_CB we find I_C
\({ I }_{ C }\cong { I }_{ C }\frac { 2-{ V }_{ BE } }{ { R }_{ 2 } } =\frac { 2-0.7 }{ 1k\Omega } \)
I_C = 1.3mA
V_CE = V_CC - I_C (R₁ + R₂)
= 10 - 1.3mA (10K + 1K)
V_CE = - 4.3 V
V_CE =-4.3V-0.7
V_CB = - 5V

α = 0.98
I_Cu = 0.6 μA
\(\alpha =\frac { \beta }{ 1+\beta } \)
(or)
\(0.98=\frac { 1 }{ \frac { 1 }{ \beta } +1 } \)
β = 49
I_CEO = (1 + β)I_CBO
= (1 + 49) x 0.6μA
I_CEO = 30 μA
= (1 + 49) x 0.6 μA
I_CEO = 30 μA
I_C = βI_B+ I_CEO
= 49 x 20 μA + 30 μA
I_C = 1.01 mA

Insulators:
(i) The valence band and the conduction band are separated by a large energy gap.
(ii) The forbidden energy gap is approximately 6 eV in insulators.
(iii) The gap is very large that electrons from valence band cannot move into conduction band even on the application of strong external electric field or the increase in temperature.
Metals
(i) In metals, the valence band and conduction band overlap.
(ii) Hence, electrons can move freely into the conduction band which results in a large number of free electrons in the conduction band.
Semiconductors
(i) In semiconductors, there exists a narrow forbidden energy gap (E < 3eV) between - g the valence band and the conduction band.
(ii) Free electrons are small in number, the conductivity of the semiconductors is not as high as that of the conductors.

(i) An oscillator basically converts de energy into ac energy of high frequency ranging from a few Hz to several MHz.
(ii) There are two types of oscillators
a) Sinusoidal
b) Non-sinusoidal.
(iii) Sinusoidal oscillators generate oscillations in the form of sine wave at constant amplitude and frequency.
(iv) Non-sinusoidal oscillators generate complex non-sinusoidal waveforms like square wave, Triangular - wave or Sawtooth -wave

(v) Sinusoidal oscillations can be of two types:
a) Damped
b) undamped.
(vi) If the amplitude of the electrical oscillations decreases with time due to energy loss, is called damped oscillations
(vii) The amplitude of the electrical oscillations remains constant with time in undamped oscillations.