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A laser beam is highly monochromatic, directional  and coherent and hence it can be sharply focussed for carrying out surgery.

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In broadcast communication mode, there are several receivers corresponding to a single transmitter. Examples, Radio and T.V.

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NA = µ₁(2d)^1/2 = 1.3×(2×0.01225)^1/2 =0.203

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If the output of the information source is a voice signal, to use it as input for transmitter, it should be converted into electrical energy by using a transducer (a device which can convert energy from one form to another).

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The original low frequency message signal cannot be transmitted to long distances. Therefore, at the transmitter, low frequency message signal is superimposed on a high frequency wave. This process is known as modulation.

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SOLUTION

Ozone layer absorbs high energy radiations like ultraviolet rays falling on it, while it transmits visible light and reflects infrared radiations.

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Low frequency signals cannot be transmitted over long distances. Modulation is the superimposition of low frequency signal on a high frequency carrier signal. Thus, modulation facilitates the transmission of low frequency signals over long distances.

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Short waves have the frequency range of 2MHz to 20MHz. These waves can be reflected to earth by a layer of atmosphere called ionosphere. Hence we can use these waves for long distance radio transmission.

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The length of the dipole antenna will be equal to / 2.

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The total spread of a signal over a range of frequencies is called its bandwidth.

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The power radiated by an antenna is related to wavelength by relation,

 P  ( 1 / ²).

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For digital communication we prefer pulse code modulation (P.C.M).

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The number of samples taken per second for a given analog signal is called its sampling frequency.

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a) The temperature of earth will decrease since the greenhouse effect will not take place in absence of atmosphere.
b) Range of radiowaves will decrease since reflecting layer(ionosphere) will be absent.

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The coverage area is given by,

 d= ( 2hR )^1/2, where h=Height of the tower and R=radius of earth.

d= ( 2 x 80 x 6.4 x 10⁶ )^1/2 = 22627.5 m = 22.62 km.

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Geostationary satellite: The satellite which appears to be at a fixed position to an observer on earth is called geostationary satellite.

The two characterstics of geostationary satellite are given as follows:

1. It remains at a height of about 36,0000 km above the equator of earth.
2. Its period of revolution should be equal to rotation of earth about its own axis i.e. 24 hours.  

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The two advantages of optical fibre communication are given as follows:-
1. It can carry large amount of information signals at once.
2. It is able to carry even the high bandwidth carrier signals.

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The four primary constants of a transmission line are given as follows:-

1. Resistance(R).
2. Inductance(L).
3. Capacitance(C).
4. Conductance(G).

SOLUTION

Length of dipole antenna = / 2-----I.

We are given with the frequency of carrier wave, evaluate wavelength from it by relation,

= c / f = ( 3 x 10⁸ ) / ( 6 x 10⁸ ) = 0.5 m.

Substituting the above value in equation I we get,

Lemgth of dipole antenna=(0.5 / 2) = 0.25 m.

SOLUTION

 In this type of communication the radiowaves transmitted and directed towards the sky are reflected back to earth at a distant location by the help of layer of atmosphere, also called as ionosphere.
The signal transmitted in this case must belong to the frequency range between 1710 kHz to 54 MHz. These waves are also called as short waves and are used for the transmission of radio signals. Ionosphere is the uppermost layer of the earth’s atmosphere and is located at the altitude of 65 km to 400 km. It contains ionized layers of electrons and ions, which are responsible for reflecting the transmitted signal back to earth. The signals which are above 54 Mhz escapes ionosphere and are not reflected back. Hence we can say that only a range of frequencies can be transmitted back towards earth. 

SOLUTION

The steps involved in converting analog signal into digital signal is shown below with the help of block schematic below,




Pulse Amplitude Modulation: In pulse amplitude modulation the pulses of the carrier pulse train is varied in accordance with the instantaneous value of the modulating signal.
Here from the figure below we can say that in pulse amplitude modulation the amplitude of pulses increseases or decreases in accordance with the modulating signal. In case of the pulse amplitude modulation the modulating signal is mixed with the modulating information signal to get the train of pulse amplitude signals. The pulse amplitude signal may be of single polarity or double polarity. If the train of pulses exists only in one direction than it is double polarity type P.A.M and if the pulses are present in both direction then it is called as double polarity P.A.M.

SOLUTION

 The communication of signal between transmitter and receiver with the help of satellite is called as satellite communication.
Working: A satellite receives the signals from earth (which is beamed by transmitter), processes the signals and transmits them back to earth. The signal beamed by the satellite is received back on a distant location on earth, from which the original information signal is extracted by the process called demodulation.
The frequency at which satellite receive the signal is called as uplink frequency while the frequency at which satellite returns the signal towards earth is called as downlink frequency. The downlink frequency and uplink frequency are different so that there is no interference between these two signals.

SOLUTION

The merits of satellite communication are given as follows:
1. It has a wide coverage area as compared to other communication systems.
2. Transmission of data at very high rate is possible through satellite communication.
3. Communication can be done from any part of earth just by using three geostationary satellites.
4. Communication done by the help of a satellite is much cheaper than other available means.
Demerits of satellite communication are given as follows:
1. The cost of launching satellite is very high and needs lot of technology expertise.
2. Every satellite has got its own time frame of working, after which it expires.
3. If there anything goes wrong in the satellite then there is no way we can fix the problem.
4. There is time delay between transmission and reception of signals, since they have to travel long distance(2x36,000=72,000 km).

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Remote Sensing: Remote sensing is a technique by which we can obtain information about a particular geographical area or object, from a distance without being in physical contact.
Applications of remote sensing: The applications of remote sensing are given as follows:-
1. By the help of remote sensing we can find out the information of cultivation of different crops in a particular area.
2. It is used in study and making of different kinds of maps also knowm as cartography.
3. It is used in oceanography i.e. for knowing the climatic condition, temperature and also to identify the potential fishing zones.
4. Remote sensing is useful in finding out the extent of pollution in any particular region and its sources too.
5. Remote sensing is used in predicting the temperature and weather and other climatic condition of a given area in advance.
6. It is also used during the period of natural calamities to assess the damage caused.
7. Remote sensing is used for spying in the field of defence and during war to locate the enemies.
8. It is used in the field of forestry. Remote sensing can give information about extent of forest cover, density of forest and types of plants. It is also helpful in detection and prevention of forest hazards like fire, excessive falling of of trees, etc.

SOLUTION

The variation of the amplitude of a carrier wave in accordance with the instantaneous value of the modulating(information) signal is called as amplitude modulation. The concept of generation of amplitude modulated signal is shown in the figure below,

Here the instantaneous value of the modulating signal is given by equation,

 e_m=E_msin_m t------(I) ;where, _m is the angular frequency of the modulating signal.

Similarly the instantaneous value of the carrier signal is given by,

 e_c=E_csin_ct--------(II) ;where, _c is the angular frequency of the carrier signal.

Modulation Index: The ratio of amplitude of modulating signal to the amplitude of carrier is called as modulation index. It is also called as degree of modulation or depth of modulation. It is denoted by m_a.

 Here we have to find the expression for the ratio E_m/E_c.

From fig(b), it follows that:-

 E_m= (E_max - E_min)/2     ----------(III)

Similarly,

E_c= E_max - E

Subsituting the value of E_m from equation (III), we get:-

 E_c= E_max -  (E_max - E_min)/2

 E_c= (E_max - E_min)/2    ------------(IV)

Dividing equation (III) by (IV),

m_a = E_m/E_c = (E_max - E_min)/(E_max + E_min)

SOLUTION

A structure is declared using keyword struct. 

For example : 

struct student
{
   int class;
   int rollno;
   float marks;
   char grade;
};

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&::i is a illegal declaration used in the code.

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“ string.h ” header file defines string functions in it like strlen, strcpy etc. These functions cannot be used without using string.h header file.  

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“ :::: ” does not exist in C++ and it will give illegal structure declaration.

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The for loop prints values of i from 1 to 10. 10 will be printed twice.

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Integer takes 2 bytes of memory and char takes 1 byte of memory in C++.  A variable within a single code represent a character.

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:: is a scope resolution operator, which is used to access global value of i.

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The value of p is assigned to pointer q . So initially *p and * q will point to the same string, i.e., abc.

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Here, j is a reference to i. If we assign value of p to j, then i will also start pointing to the value of p, i.e., 10.

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A pointer points to the address of a variable. It cannot be used as integers.

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Here, j and k are not being declared before using assignment operation. The correct way is int i, j ,k; to be used before assignment.

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res-- is a post decrement operator. First it will print the value and then the value will be decreased by 1. ++res is a pre increment operator, it will first increment the value and then print the result.

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A reference has to be properly initialized, otherwise it will result in an error. In C++, special care is taken for assignment of void pointers to other pointer types. While we can assign a pointer of any type to a void pointer, the reverse is not true until we do explicit typecasting.

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A type of polymorphism where different functions with the same name are invoked based on the data types of the parameters passed is called overloading.

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In C++, void pointer cannot be assigned to the pointer of any type. This would result in an error of type mismatch. It can be made true when we explicitly typecast it, b=(char*) a;

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This is legal in C++ but not in C. Unions, which do not have a class name, are anonymous union.

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One variable is declared when structure is defined without a tag.

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The function gets() is a string function that reads a string i.e. multiple characters from the keyboard including white spaces etc.

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The get() function is an input function. It fetches the character from the keyboard and stores it in a character variable.

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The function getline() is invoked using cin. Example cin.getline(string1,50). String1 is the name of the array and 50 is the number of characters, we want this function to read.

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The stdio.h is a standard input output header file. These have libraries of code which we may insert in the program, by using as a reference in the top block.

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fstream is an input-ouptput functions of stream class. It provides support for simultaneous input and output operations.

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The term conio.h is a console input output header file. These have libraries of code which we may insert in the program, by using as a reference in the top block.

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getline(), putline(), get() and put() functions are unformatted stream of functions in header file, i.e., iostream.h, whereas gets() and puts() are string functions in stdio.h.

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The post-increment operator first prints the value and then increments, whereas the pre-increment operator first increments the value then print.

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According to the precedence of operators, bracket will be evaluated first.

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Run time error is an error that occurs during the execution of a program. The compilation is not affected by it.

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Real constants are numbers having fractional parts. These may be written in fractional form or exponent form. It must have at least one digit before decimal and one digit after decimal and commas are not allowed.

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Keywords are not acceptable as identifier in C++. break is a keyword.

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if statement tests a particular condition; if the condition evaluates to true then action is performed otherwise action is ignored.

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sizeof() operator accepts one parameter which can either be a type or a variable itself and return the size in bytes of that type or object.

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OOPs programs are built from reusable software components. It saves time and is easier to work with.

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'n' sends the new line character but does not flush the output buffer.

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An empty class has no variable declarations, no functions or methods but objects of these classes can have a non–zero size.

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Correct sentence is cout < < " computers can be fun ” ;

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clrscr() is a console input output function which is defined in conio.h header file.

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Interface generally refers to an abstraction that an entity provides of itself to the outside. This separates the methods of external communication from internal operation and allows it to be internally modified without affecting the way outside entities interact with it, as well as provide multiple abstractions of itself.

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We can create two or more references for the same variable but same reference can not be tied with several variables.

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In dynamic memory allocation, whenever the object is out of scope, its memory would be freed and deallocated. So, a destructor is automatically invoked by the class.

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Abstract classes are classes, which cannot be instantiated but they can have sub classes. They do not have method definitions but the prototypes and declarations can be done.

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A constructor is a special member function, which will construct an object with user-defined values, whenever an object is created. It is a special method used in OOP, which puts the object member into a valid state.

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Inheritance graph (also known as derivation graph) is the chain depicting the derivation of a class from multiple base classes.

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The velocity of electromagnetic waves (T.V. wave, microwave, radio wave etc.) is 3  10⁸ ms^-1. On the other hand, the velocity of sound waves is 332 ms^-1. Therefore, sound wave is unable to transmit intelligence to far off places.

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Along the channel, a transmitted signal may get distorted due to channel imperfection and noise may add to it. The receiver, therefore, gets a corrupted version of the transmitted signal. The receiver operates on the received signal before delivering the signal to the user of the information.

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f_SB = f_c ±f_m = 1000 ± 0.6       = 1000.6 kHz and 999.4 kHz

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SOLUTION

Energy flux = Power / area = 10¹⁷ W/cm²

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SOLUTION

The radio waves of frequency 300 MHz to 3000 MHz belongs to Ultra high frequency band.

SOLUTION

Optical fibre is always preferred over copper wires for transmission as fibres is very less and it can take large number of telephonic message at a time.

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For the transmission of audio signals ,high frequncy carrier wave is used as they can ttravel through the space or medium with th espeed of light and they are not obstructed by earth`s atmospere.

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The loss of kinetic energy of the wave while passing through the lower ionosphere layer is inversely proportional to the square of the frequency.

SOLUTION

The electrical conductivity of earth’s atmosphere increases with altitude because the high energy particles coming from outer space while entering earth’s atmosphere cause ionization of the atoms of the gases present in the atmosphere and their energy decreases as they approach to earth.

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In the process of demodulation, carrier wave and modulating waves get separated.

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_c - _m and _c + _m are respectively called the lower side and upper side frequencies. The modulated signal now consists of the carrier wave of frequency _c plus ten sinusoidal waves each of frequency slightly different from, known as side bands

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The transmitted message gets attenuated in propagating through the channel. The receiving antenna is therefore to be followed by on amplifier and a detector. In addition, to facilitate further processing, the carrier frequency is usually changed to a lower frequency because the detected signal may not be strong enough to be made use of and hence is required to be amplified.

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As long as the broadcast frequencies are sufficiently spaced out so that sidebands do not overlap, different stations can operate without interfering with each other.

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In case of amplitude modulation  = A_m/A_c.  is kept  1 to avoid distortion.

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Interference, an undesirable effect in signal transmission, occurs most often in radio transmission whose receiving antennas usually intercept several signals at the same time.

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Distortion is waveform perturbation caused by imperfect response of the communication system to the desired signal itself. Therefore, it disappears when the signal is turned off.

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Sky wave propagation is suitable in the frequency range from a few MHz to 40 MHz. 10 kHz cannot be radiated due to impracticable antenna size while 1 GHz and 1000 GHz will penetrate the atmosphere.

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The degree of ionisation of atmosphere varies with height due to the variation in solar radiation and molecular concentration. The density of atmosphere decreases with height. Although the solar radiation is intense at higher altitude, there are few molecules to be ionised. Near the earth’s surface, the molecular concentration is high but the solar radiation is low; hence, low ionisation results. The degree of ionisation is therefore highest at the intermediate heights.

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