Communication Systems Questions and Answers

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Percentage error in the determination of g is If velocity of light in vacuum 3 x 108 m s acceleration due to gravity 9 81 m s2 and density of mercury 13600 kgm be adopted as the fundamental units choose the correct option s a unit of mass is 1 05 x 1052 kg b unit of length is 9 17 x 10 5 m

Find 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 end are 0 1 m and 0 04 m and the pressure drop

A microwave telephone link operating at the central frequency of 10 GHz has been established If 2 of this di is available for microwave communication channel then how many telephone channels can be simultaneously granted if each telephone is alloted a bandwidth of 10 KHz a 2 104 c 5 x 107 b 104 d 6 10 9 10 11

A solid cylinder of mass m length I and area of cross section A is placed as shown in the figure If Young s modulus is Y then strain energy stored in the cylinder is A C 2 m g l 3AY 2 m g 1 7 A V B D m g 1 6AY m g 1 AY

Two particles of masses 2 g and 36 g respectively are attached to two ends of a rigid light rod of length 1 9 m The centre of the mass of the system from 2 g particle is nearly at distance of 1 4 m 1 8 m 1 7 m 0 95 m

Determine the output voltage of a differential amplifier for the input voltage of 300 micro volt and 240 micro volt The differential gain of the amplifier is 5000 and value of CMRR is a 100 b 100000

A signal of frequency 20 kHz and peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1 2 MHz and peak voltage 25 Volts Choose the correct statement A Modulation index 5 side frequency bands are at 1400 kHz and 1000 kHz B Modulation index 5 side frequency bands are at 21 2 kHz and 18 8 kHz C Modulation index 0 8 side frequency bands are D 180 kHz and 1220 kHz Modulation index 0 2 side frequency bands are at 1220 kHz and 1180 kHz

Which among the following statements is correct regarding the dependence of voltage gain of an amplifier on the frequency of the signal A the signal does not depend upon frequency of Your Answer B signal increases with frequency of the decreases with frequency of the signal D with frequency of the signal initially constant and then decreases

The figure shows a digital circuit constructed using negative edge triggered J K flip flops Assume a starting state of Q2Q Q0 000 This state will repeat after how many number of the cycles of the CLK 1 Jo Qo Clock clock 1 Ko Qo J clock 1 K Q1 Q J clock 1 K Q2 Q