# Communication Systems Questions and Answers Physics
Communication Systems
The two sections of an 11 kV busbar are connected by a reactor with a through load rating of 25 MVA and a reactance phase of 10 based on 25 MVA Each section is connected by a 20 MVA transformer having a reactance of 10 on 20 MVA to a 33 kV busbar which is not sectionalized Connected to this 33 kV busbar are two generator transformer sets each rated at 37 5 MVA and each having a total reactance of 25 on 37 5 MVA The 33 kV busbar is connected to the 132 kV grid bus by two identical transformers in parallel each rated at 45 MVA and having a reactance of 12 5 on 45 MVA The 3 phase fault level infeed from the grid is 2000 MVA a Calculate the 3 phase fault level MVA at the 11 kV busbar with and without the reactor reactor short circuited and at 33 kV busbar Physics
Communication Systems
17 When a low lying aeroplane passes overhead e sometimes notice a slight shaking of the picture on ur TV screen This is due to a diffraction of the signal received from the antenna b interference of the direct signal received by the antenna with the weak signal reflected by the passing aircraft c change of magnetic flux occurring due to the passage of aircraft d vibrations created by the passage of aircraft Physics
Communication Systems
Choose the basic condition to be satisfied for the transmission of light through an optical fibre i Light must travel from denser to rarer medium ii Light must travel from rarer to denser medium iii Light must travel in same medium iv Angle of incidence in the denser medium must be lesser than the critical angle v Angle of incidence in the denser medium must be greater than he critical angle vi Angle of ncidence in the denser nedium must be equal to ritical angle i and iv only iii and vi only i and v only ii and vi only 1 point Physics
Communication Systems
12 The amplifiers A B and C are connected in series If the voltage gain of A B and C are 10 15 and 20 respectively and input signal 2 mV peak value Then the output signal voltage s peak value will be 1 6 V 2 5V Physics
Communication Systems
A parallel plate capacitor without dielectric is charged by a battery and kept connected to the battery A dielectric slab of dielectric constant K is inserted between the plates fully occupying the space between the plates The energy density of electric field between the plates will 1 Increase K2 times 2 Decrease K times 3 Increase K times Physics
Communication Systems
m The process of superimposing a low frequency signal on high frequency carrier wave for long distance transmission is known as a demodulation c amplification b modulation d attenuation Physics
Communication Systems
9 A liquid drop of radius R breaks into 64 tiny drops each of radius r If the surface tension of the liquid is T then the gain in surface energy is 1 48 r T R 48 2 12 T S Eny ST A 96 r T 192 r T s 402T TR 47 8 4 2TR 15 Physics
Communication Systems
In the figure shown the switch is closed at t 0 The potential difference across the resistance R 2052 1 millisecond after closing the switch is K e Find the value of K HH 40 f 20V R 20 100 r 100 Physics
Communication Systems
An ideal diatomic gas undergoes a process AB for which PV indicator diagram is shown Temperature at state A is To When process changes from endothermic to exothermic temperature of the gas is 175x 864 To Find the value of a Physics
Communication Systems
Three identical metallic plates are arranged at small separations as shown figure The outer and inner plates are given charges as indicated If the mount of charge in C that will flow through the switch S when it is closed is 10 k then find the value of k 30 C 20 C 164 20 30 C Physics
Communication Systems
Consider a uniform circular disc M R having a point mass M at its circumference Disc is rolling over a rough horizontal surface consider the arrangement shown in the position At this position a is the acceleration of centre of disc wo and a are the angular velocity and angular acceleration of disc at this instant Now choose the correct option s Disk M R If o a M 2a direction of frictional force will be forward VR If If oo R 2a direction of frictional force will be forward N normal reaction from ground 2 Mg N normal reaction from ground 2 Mg Physics
Communication Systems
The figure below shows a drop of mercury on a glass surface The radius of curvature of the drop at its upper point is R 1 7 mm What is the mass m in mg of the drop if its height h 2 mm the contact radius of the drop with the horizontal plane on which it is located is equal to r1 mm The density of the mercury is p 13500 kg m the surface tension of mercury is a 425 mN m Take g 10 m s m Write to its nearest integer Take contact 11 angle as 180 R H Physics
Communication Systems
In the following sequential circuit the initial state before the first clock pulse of the circuit is Q Q0 00 The state Q Q0 after the 333rd clock pulse is CLK Jo Qo Ko Qo J Q K Q Physics
Communication Systems
A telephonic communication service is working at carrier frequency of 10 GHz Only 10 of it is utilized for transmission How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of 5 kHz A B C 2 x 10 2 x 10 2 x 10 Physics
Communication Systems
For ground wave transmission which of the following is true A B C size of antenna should be comparable to wavelength antenna comparable to wavelength radiate signals with high frequency only a Physics
Communication Systems
An ideal diode D and a resistance R are connected in series with an alternating voltage 0 source V t V sin ot If the root mean square value of the voltage V is measured at the point X as shown the result will be A Vo 0 B C V V sin ot D R OX Physics
Communication Systems
For the shown transistor current amplification factor B 45 and voltage drop across load resistance 1 k0 is 1 volt Then the base current is O 0 016 MA O 0 022 MA O 0 152 mA O 0 097 mA Physics
Communication Systems
estion 3 After traveling a distance of 20 m along a transmission line the voltage wave remains 13 of it s source amplitude What is the attenuation constall 0 1 NP m O 0 15 NP m 0 045 NP m 0 08 NP m Physics
Communication Systems
A transmission line operating at 5GHz frequency has characteristic impedance Z0 800 and the phase constant B 1 radim The inductance per unit length of the transmission line will be 3 81nh m 2 54nH O Physics
Communication Systems
For the shown transistor current amplification factor 45 and voltage drop across load resistance 1 k is 1 volt Then the base current is VB O 0 016 MA O 0 022 MA www 1 ks Load resistance Physics
Communication Systems
20 The antenna current of an AM transmitter is 8A when only the carrier is sent but it increas to 8 93A when the carrier is sinusoidal modulated what will be the antenna current when depth of modulation is 80 1 8 8 A 2 9 19 A 3 9 91 A 4 10 A Physics
Communication Systems
Assertion When two waves interfere one wave alters the progress of the other wave Reason In interference there is no loss of energy O Both Assertion and Reason are correct and Reason is the correct explanation of Assertion Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion Assertion is correct but Reason is incorrect Both Assertion and Reason are incorrect Physics
Communication Systems
pe of question 1 75mA 39 For this truth table A 0 0 1 1 B 0 1 0 1 2 20mA Y 1 0 0 1 3 100mA 4 25mA C Physics
Communication Systems
Explain the differences between polling and interrupt based systems b Consider a uniprocessor system that can run one task at a time We install this processor in a thermal plant to respond to unexpected events The processor is programmed to respond to excess temperature T and pressure P Safety standards require that the response time of the processor shouldn t exceed 1 ms if one or both the mentioned events occur simultaneously Which method polling or interrupt would be preferred if the response time has to be guaranteed to not exceed 1 ms Physics
Communication Systems
The T V transmission tower in delhi has a height of 240 m the distance upto which the broadcast can be received taking the radius of the earth to be 6 4 x 106 m A 100 km B 60 km C 55 km D 50 km Physics
Communication Systems
An uninsulated chilled water pipe carrying water at 2 C passes through a hot humi factory area where the temperature is 35 C and the relative humidity is 80 percen because of steam operated equipment in the factory If the pipe is 5 cm in diamete and the exposed length is 7 5 m estimate the condensate that will drip off the pipe For this estimate assume that the pipe is exposed to saturated vapor at the partial pressure of the water vapor in the air Physics
Communication Systems
A 4 bit serial in parallel out shift register is used with feedback as shown in fig the shifting sequence is QAQB Qc QD After how many clock pulses register comes to initial state CLK Shift register Serial in QA QB Qc Qc QD Physics
Communication Systems
Ve crc PO EF H OF The logic circuit shown has the input waveforms A and B as shown Pick out the CORRECT output waveform US A B Input A Jo Input B O A Y THE Your Answer Physics
Communication Systems
Multiplexing is the generic term used to describe the operation of sending one or more signals over a common transmission line at different times or speeds and the device we use to do just that is called a Multiplexer The multiplexer shortened to MUX or MPX is a combinational logic circuit designed to switch input lines through to a output line by the application of a control signal Multiplexers control multiple input lines called channels to the output Multiplexers or MUX s can be made of MOSFET S or relays or current input X In the given 4 to 1 multiplexer if c1 0 and c0 1 then the output M is a XO b X1 X2 M Physics
Communication Systems
Q 23 The output characteristics of a transistor is shown in the figure When VCE is 10 V and le 4 0 mA then value of Bac is Ic in mA 00 2 4 6 8 10 12 14 VCE in volts 60 A 50 A 40 A 30 A 20 A 10 A Physics
Communication Systems
98 along the string is always that of a harmonic oscillation Problem 4 23 Problem 4 1 Show that the choice of new normal coordinates X and Y expresses equations 4 3a and 4 3b as equations 4 4a and 4 4b Problem 4 2 Express the total energy of Problem 4 1 in terms of the pendulum displacements x and y as E Ekin Epot x Ekin Epot Epot xy where the brackets give the energy of each pendulum expressed in its own coordinates and Epot xy is the coupling or interchange energy involving the product of these coordinates Problem 4 3 Figures 4 3 and 4 5 show how the pendulum configurations x 2a y 0 and x 0 y 2a result from the superposition of the normal modes X and Y Using the same initial conditions and Coupled Oscillations x 2a y 0 x y 0 draw similar sketches to show how X and Y superpose to produce x 2a y 0 and x 0 y 2a Problem 4 4 In the figure two masses m and m2 are coupled by a spring of stiffness s and natural length 1 If x is the extension of the spring show that equations of motion along the x axis are m x1 Sx m x 2 sx and combine these to show that the system oscillates with a frequency where w X l m S fl m1m2 m m Mass of Na atom 23 a m u Mass of Cl atom 35 a m u 1 a m u 1 67 10 27 kg y is called the reduced mass The figure now represents a diatomic molecule as a harmonic oscillator with an effective mass equal to its reduced mass If a sodium chloride molecule has a natural vibration frequency 1 14 x 10 3 Hz in the infrared region of the electromagnetic spectrum show that the interatomic force constant s 120 Nm this simple model gives a higher value for s than more refined methods which account for other interactions within the salt crystal lattice mmmmmm m X 120 579 S 2m Problem 4 5 The equal masses in the figure oscillate in the vertical direction Show that the frequencies of the normal modes of oscillation are given by w 3 5 and that in the slower mode the ratio of the amplitude of the upper mass to that of the lower mass is 5 1 whilst in the faster mode this ratio is 5 1 Physics
Communication Systems
The time delay between transmission and the arrival of the reflected wave of a signal using ultrasound traveling through a piece of fat tissue was 40 s At what depth did this reflection occur Select one 12 um O 3 mm O 6 cm O3 cm Physics
Communication Systems
Which is the main relay for protecting up to 90 of the transmission Line length in the forward direction 1 Directional over current relay 2 Mho relay Physics
Communication Systems
A lossless transmission line having surge impedance loading SIL of 2280 MW A series capacitive compensation of 30 is emplaced Then SIL of the compensated transmission line will be 1 2 1835 MW 4 2280 MW 3 2725 MW 3257 MW Physics
Communication Systems
Two identical antennas mounted on identical towers are separated from each other by a distance of 45 km What should nearly be the minimum height of receiving antenna to receive the signals in line of sight Assume radius of earth is 6400 km A B 158 2 m 79 1 m Physics
Communication Systems
If the density DALTON S LAW OF PARTIAL PRESSURE A gaseous mixture is prepared at 100 kPa and 25 C by mixing 0 2 g of hydrogen 2 8 g of nitrogen and 1 6 g of oxygen Calculate 9 10 i Mole fraction ii Partial pressure of each component contains 20 of hydrogen by mass What is the partial Physics
Communication Systems
6 8 A cylindrical rod of steel E 207 GPa 30 106 psi having a yield strength of 310 MPa 45 000 psi is to be subjected to a load of 11 100 N 2500 lb If the length of the rod is 500 mm 20 0 in what must be the diameter to allow an elongation of 0 38 mm 0 015 in Physics
Communication Systems
Regarding brown ring complex formation which of the following statement is wrong 1 NO formation takes place 2 Fe SO is uses in this process 3 Fe 2 and NO both are reduced 4 Formula of brown ring complex is Fe H O NO1 2 Physics
Communication Systems
2 Derive an expression for the COP of an ideal gas refrigeration cycle with a regenerative heat exchanger Express the result in terms of the minimum gas temperature during heat rejection Th maximum gas temperature during heat absorption T and pressure ratio for the cycle T P P Ans COP h p Physics
Communication Systems
A ground receiver station is receiving a signal at 100 MHz transmitted from a ground transmitter at a height of 300 m located at a distance of 1000 km It is coming via 1 Ground wave 2 Space wave 3 Sky wave Physics
Communication Systems
A ground receiver station is receiving a signal at 500 MHz transmitted from a ground transmitter at a height of 300 m located at a distance of 500 km It is coming via 1 Ground wave 2 Space wave 3 Sky wave MA communication Physics
Communication Systems
1 An information signal of 150 MHz is to be sent across a distance of 40 km Which mode of communication is suitable 1 Ground wave propagation 2 Space wave propagation 3 Sky wave propagation Physics
Communication Systems
1 A modulating signal 20 sin 2 x 10 t is used to modulate a carrier sign 40 sin 2 x 10 t Find the Modulation index Percentage modulation Frequencies of the sideband components and their amplitudes Bandwidth of Modulating signal Physics
Communication Systems
The concept of an electricity short medium and long line is primarily based on the 1 Nominal voltage of the line 2 Physical length of the line 3 Wavelength of the line Power transmitted over the line Physics
Communication Systems
Which of the following statements regarding optical sensors is false A An optical fiber can carry light received at a limited range of angles B All optical sensors use optical fibers C The range of a fiber optic spectrophotometer is obtained using multiple gratings D None of the above Physics
Communication Systems
83 The following Figure shows a logic gate circuit with two inputs A and B and the output Y The voltage waveforms of A B and Y are given 2011 A B A B 0 1 1 Y 0 Logic gate circuit The logic gate is a NAND gate c OR gate 13 14 b NOR gate d AND gate Physics
Communication Systems
33 From a circular disc of radius R a triangular 33 portion is cut see fig The distance of COM of the remaining disc from centre of disc O is 4R 1 3 x 2 3 2R 3 2 450 45 C SR 2 7 2 R 3 1 quien e feel all fa 1 3 4R 3 2 45 2R 3 2 Physics
Communication Systems
A conical hole is machined in a block of metal whose emissivity is 0 5 The hole is 2 5 cm in diameter at the surface and 7 5 cm deep If the metal block is heated to 800 K calculate the radiation emitted by the hole Calculate the value of an apparent emissivity of the hole defined as the ratio of the actual energy emitted by the hole to that energy which would be emitted by a black surface having an area equal to that of the opening and a temperature equal to that of the inside surfaces Physics
Communication Systems
QUESTION A25 1 mark The velocity of an object is expressed as a graph in the figure below Determine the displacement of the object from t 3 s to t 10s v m s a 48 m b 43 8 m c 33 8 m 8 7 8 n 3 2 1 1 2 3 4 5 6 7 8 9 10 11 760 d 39 m e None of the above Physics
Communication Systems
7 57 Calculate the rate of flow of glycerine of density 1 25 10 kg m through the conical section of a pipe if the radii of its ends are 0 1 m and 0 04 m and the pressure drop across its length is 10 N m Ans 6 44 10 m s