(i) For children, T.V. is a boon, because it is a source of knowledge, information and lot of entertainment.
(ii) Elderly people have reservations about the T.V. because all sorts of programmes including Adult channels, fashion channels, horror shows, etc. are telecast. They feet that children are immature and their minds get impregnated with wrong values. The television consumes lot of time, disconnects them from society and leaves little time for their studies.
(iii) Personally, I feel we have to strike a balance between the views of children and the views of elderly people. Too much of everything is bad and children must be guided to view educative programes (e.g. on discovery channel, National geographic channel, etc.), News channels, Comedy programmes for a limited time of 1-2 hours a day. This will make them more knowlegable and also save their precious time for studies.

Microwaves are the electromagnetic waves of wavelength of the order of a few millimeters, which is less than those of T.V. signals. On account of smaller wavelength, the microwaves can be transmitted as beam signals in a particular direction, much better than radiowaves because microwaves do not spread or bend around the corners of any obstacle coming in their way. Therefore, microwaves are better carriers of signals than radio waves.

Active satellite is that satellite which carries equipments like antenna system, power supply, receiver and transmitter. It receives the UHF or microwave signal from the earth station, processes it, amplifies it and then retransmits it towards earth at different frequency. Thus active satellite works as an active microwave repeater in the sky, called transponder. Apart from it, an active satellite also carries different types of sensors (i.e. camera, an infrared scanner, microwave scanner, etc) which transmits information (in the form of data and pictures) to the earth stations.
A passive satellite is nothing but a metal-coated plastic ballon or metallic sphere which works as a reflector to the signals back to the earth. A passive satellite does not carry those equipments which are being carried by active satellites.

If \(v\) kHz is maximum modulating frequency permissible, then bandwidth required for each sttation = 2v.
\(\therefore Number \ of \ stations=\frac { total \ band \ width }{ 2v }\)
\(10=\frac { 100 \ kHz }{ 2v }\)
\( \\ v=\frac { 100 }{ 1\times2 } =5 \ kHz\)

Maximum amplitude, A_max = 10 V
Minimum amplitude, A_min = 2 V
Modulation index μ, is given by the relation:
\(\mu=\frac{A_{\max }-A_{\min }}{A_{\max }+A_{\min }}\)
\(=\frac{10-2}{10+2}=\frac{8}{12}=0.67\)
if A_"min" = 0
Then \(\mu=\frac{A_{\max }}{A_{\max }}=\frac{10}{10}=1\) 

\({ m }_{ a }=\frac { { E }_{ max }-{ E }_{ min } }{ { E }_{ max }+{ E }_{ min } } \)
\(Here\quad { E }_{ max }={ E }_{ c }+0.5{ E }_{ c }=1.5{ E }_{ c }\)
\(\ { E }_{ min }={ E }_{ c }-0.5{ E }_{ c }=0.5{ E }_{ c }\)
\(\\ \therefore \ \ { m }_{ a }=\frac { 1.5{ E }_{ c }-0.5{ E }_{ c } }{ 1.5{ E }_{ c }+0.5{ E }_{ c } } =0.5\)

Modulation index is defined as the ratio of amplitude of modulating signal and amplitude of carrier wave
Alternatively,
 \(\mu =\frac { { A }_{ m } }{ { A }_{ c } } \)
The amplitude of modulating signal is kept less than amplitude of carrier wave to avoid/ minimize distortion/noise.

Space wave propagation.
Range of frequencies for space wave propagation is used to transmit
VHF band   30MHz to 300 MHz
UHF band   300MHz to 3 GHz
Microwaves 100 GHz
e.g. TV signals 80 to 200 MHz and RADAR beans (microwaves).

For F₁ layer : 5 x 10⁶ = 9 (N_max)^1/2 or \({ N }_{ max }=\left( \frac { 5 }{ 9 } \times { 10 }^{ 6 } \right) ^{ 2 }=3.086\times { 10 }^{ 11 }{ m }^{ -3 }\)
For F₂ layer : 8 x 10⁶ = 9(N_max)^1/2  or  \({ N }_{ max }=\left( \frac { 8 }{ 9 } \times { 10 }^{ 6 } \right) ^{ 2 }=7.9\times { 10 }^{ 11 }{ m }^{ -3 }\)

The electromagnetic waves of frequency less than 30 MHz (or wavelength  10 m or more ) form amplitude modulated range (i.e. A > M range) These waves atmosphere of the earth. But these waves are reflected back by the topmost layer of the atmosphere, the ionosphere.

(a) The ultra-high frequency em radiations, continuously emitted by a mobile phone, may harm the system of the human body.
(b) Sister Anita shown
(i) Concern about her brother
(ii)  Awareness about the likely effects of em radiations on human body
(iii) Sense of responsibility   any two)
(c) The sidebands are
\(({ V }_{ c }+{ \upsilon }_{ m }) \ and \ ({ V }_{ c }-{ \upsilon }_{ m })\)
\(or \  (1000 \  + \  10) \  kHz \  and \  (1000 \  - \  10) \ kHz  \)
\(1010 \ kHz \ and \ 990 \ kHz\)

Here, h = 300 m ; R = 6.4 x 10⁶ m ; N_max = 10¹² m^-3
For space wave propagation, Maximum distance covered by space wave communication, 
\(d=\sqrt { 2Rh } =\sqrt { 2\times 6.4\times { 10 }^{ 6 }\times 300 } \)
 \(=61.96\times { 10 }^{ 3 }\approx 62 \ km\)
Since the distance between transmitter and receiver is 100 km, hence for the given frequency signals of 6.0 MHz and 110 MHz, the propagation is not possible via space wave propagation.
For sky wave propagation, the critical frequency, 
\({ v }_{ c }=9\left( { N }_{ max } \right) ^{ 1/2 }=9\times \left( { 10 }^{ 12 } \right) ^{ 1/2 }=9\times { 10 }^{ 6 }Hz\)
 = 9 MHz
Since the frequency of signal (a) i.e. 6.0 MHz is less than v_c , so its propagation via sky wave is possible. Since the frequency of signal (b) i.e. 110 MHz is greater than v_c  hence its propagation is not possible via sky waves. For that, satellite communication is used.