EC Objective Paper I (Set - D)

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2 EC-Objective Paper-I ESE-5 EC Objective Paper I (Set - D). If a system produces frequencies in the output are not present in the input, then the system cannot be Minimum phase system (C) Stable and causal Linear shift invariant Stable and linear Since linearity and time-invariance (shift-invariance) doesn t effect the frequency of input to get the output the system can t be LTI.. In eddy current damping system, the disc employed should be of Conducting and magnetic material Conducting but non-magnetic material (C) Magnetic but non-conducting material Non-conducting and non-magnetic material 3. Which of the following can act as in inverse transducer? LVDT Strain (C) Piezo electric crystal Bimetal strip (C) 4. Which one of the following thermocouple pairs has maximum sensitivity around 73 K? Nichrome-constant Copper-Nickel (C) Platinum-constantan Nickel-constantan 5. Maximum power will be delivered from an ac source to a resistive load in a network when the magnitude of the source impedance is equal to Half the load resistance (C) The load resistance The equation of power for resistive load is P RL V S ZS RL R L So we can say power is maximum when Z S =, Double the load resistance Zero Note that maximum power transfer theorem is not applicable here as we are not calculating the value of R L (variable). We are going in reverse way. 6. The dc resistivity and permeability exhibited by a type superconductor are respectively: Zero and zero Zero and unity (C) Unity and zero Unity and Unity

3 xm r In super conductors r, xm (negative) super conductor has zero Resistivity. Directions: Each of the next Fourteen (4) items consists of two statements one labeled as the Statement (I) and the other as Statement (II). Examine these two statements carefully and select the answers to these items using the codes given below. Codes: Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) (C) Statement (I) is true but Statement (II) is false Statement (I) is false but Statement (II) is true 7. Statement (I): One of the mechanism by which a transistor s usefulness may be terminated, as the collector voltage is increased, is called punch through. Punch through results from the increased width of the collectorjunction transition region with increased collector-junction voltage. Punch through: When the base collector voltage reaches a certain (device specific) value, the base collector depletion region boundary meets the base emitter depletion region boundary. When in this state the transistor effectively has no base. The device thus loses all gain when in this state. 8. Statement (I): In ferroelectric materials, domains with permanent electric dipoles may be created that would align along external electric field. Ferroelectric materials undergo phase transformation of symmetric to asymmetric structure below a critical temperature. 9. Statement (I): Conduction takes place in an enhancement MOSFET only for gate voltages below the threshold level. V GS >V t conduction takes places V GS <V t no conduction take place in MOSFET In an enhancement MOSFET, a channel of semiconductor of the same type as the source and drain is induced in the substrate by a positive voltage applied to the gate.. Statement (I): MOSFET is a field effect transistor whose drain current is controlled by the voltage applied at the gate. MOSFET is an insulated gate FET

4 . Statement (I): All passive components can be fabricated in a single chip. As opposed to discrete circuits where all components are separately inserted and connected, in an integrated circuit, they are simultaneously created on a chip of semiconductor material during manufacturing.. Statement (I): The total energy of an energy signal falls between the limits and. The average power of an energy signal is zero. Energy signal is a signal with finite energy and zero average power. Thus statement (I) and (II). Both are correct but statement (II) is not giving explanation/reasoning to statement (I). 3. Statement (I): Sinusoidal signals are used as basic function in electrical systems. The response of a linear system to a sinusoidal input function remains sinusoidal. 4. Statement (I): Dirichlet s conditions restrict the periodic signal x(t), to be represented by Fourier series, to have only finite number of maximal and minima. x(t) should possess only a finite number of dis-continuities. Strong Dirichlet conditions states that the Fourier series exists if and only if the signal has a finite number of maxima and minima (or) finite number of discontinuities. 5. Statement (I): Ferrite cored coils are used in high frequency tuned circuits. Ferrite cored coils have high Q as compared to iron-cored coils. 6. Statement (I): A cylindrical conductor of radius R carries a current H.dl j.ds s L I H.r r R Ir H R H r statement (I) is correct I. The magnetic Field intensity within the conductor increases linearly with the radial distance r < R. The current enclosed increases as the square of the radial distance while the circumference increases linearly with the radial distance. Statement (II) is correct explanation to Statement (I).

5 I.H 7. Statement (I): Hall voltage is given by V H R H Where I is the current, H is t the magnetic field strength, t is the thickness of probe and R H is the Hall constant. (C) BI VH W R H BI So, VH R H. W W = t = width (or) thickness B H Hall effect does not sense the carrier concentration. Hall Effect measures density of the carries, and their sign (whether electron (or) holes) 8. Statement (I): For an energy meter, careful design and treatment of breaking magnet during its manufacture are essential in order to ensure consistency of break magnet during the use of meter. Steady rotational speed of energy meter disc is directly proportional to flux of the break magnet. 9. Statement (I): If the limiting errors of measurement of power consumed by and the current passing through a resistance are.5% and.% respectively, then the limiting error of resistance measurement will be.5%. Mathematically if f = xyz. Then f x yz xyz xy z It is given that the limiting error of power is Poweris.5%and Current is.% P R so the limiting error will be I.5. % 3.5%. Statement (I): Integrating DVM measures the true average value of the input voltage over a fixed measuring period. Since the display of measured signal is a decimal number, the errors due to parallax and observation error are eliminated.. Measurement of pressure can be done by using wire, foil or semiconductor type Strain Gauges. The disadvantage of the semiconductor type of strain gauge compared to other two is in terms of Gauge factor (C) Temperature sensitivity (C) Hysteresis characteristics Frequency response

6 . The Fourier series of a periodic function x T (t) with a period T is given by jko t Xske, where o T And the Fourier coefficient X s (K) is defined as, k jkot Xsk xtte dt T If xt t is real and odd, the Fourier coefficients X s (K) are Real and odd Complex (C) Real Imaginary T jkt xs k xt t e dt T T Consider Thus xs T T jkt jkt xtte dt xt te dt T k is imaginary. x t is odd, x t x t T T T T jkt jkt xsk e e xttdt T T j x k sin k t x t dt s T T 3. Consider a continuous time period signal x(t) with fundamental period T and Fourier series coefficient X[K]. What is the Fourier series coefficient of the signal y t x t t x t t?.cos Kt XK o T o o T sin Kt XK to to to to (C) e XK e X K e XK e XK y(t) = x(t-t ) + x(t+t ) x t FS x k By using time-shifting property of Fourier series, FS FS x t t x k e x t t x k e Fourierseriesof y t jkt jkt e e xk x k cosk t jkt jkt T x k cos kt o

7 4. Consider the following transfer functions:.. 3. j j j j The transfer functions which have a non linear phase are: and only and 3 only (C) and 3 only, and 3 5. A continuity equation is also called as the law of conservation of Mass Energy (C) Charge Power (C) Continuity equation is based upon the law of conservation at charge. 6. The basic structure of an avalanche photodiode is p i p n p i n (C) p p n i p n 7. Consider two infinite duration input sequences Convergence [ROC] of Z-transform of their superposition i.e. xn xn plane except possibly at Z = or Z? When their linear combination is of finite duration When they are left sided sequences (C) When they are right sided sequences When their linear combination is causal x n,x n. When will the Region of be entire Z For a finite duration sequence the ROC will be entire Z-plane except z = and/or Z. 8. If the lower limit of Region of Convergence (ROC) is greater than the upper limit of n ROC, the series XZ xnz (C) n Converges Zero (C) Does not converge None of the above z

8 If is lower limit and is upper limit of ROC then ROC is z. Accordingly, the signal corresponding to is Right-sided and the signal corresponding to is left sided. Since, it is given that, ROC does not converge. 9. For a random signal (continuous time) x(t) defined for t, its probability density function (pdf) at t = t o is such that It is non-negative and it s integral Need not be non-negative, but integral equals (C) It is non-negative, but integral is not None of the above 3. The response of a system to a complex input jt jt jt as yt t.e e. The system is definitely LTI (C) may be LTI x t e ;y t te e jt jt jt y(t) = tx(t) + x(-t) consider y(t) = y (t) + y (t) y (t) = t x(t) is linear but non-time invariant Similarly y (t) = x(-t) is also linear but non time-invariant Thus the system is non-lti. x t is definitely not-lti Information is insufficient e is specified 3. The rise time of the output response of a low pass filter circuit when a step input is applied will be Proportional to the band width (C) Half the value of band width t r.35 Bandwidth Inversely proportional to the band width of the band width 3. Consider an LTI system subjected to a wide sense stationary input xn white noise sequence. The cross correlation m is (C) x hm x hm x hm Where m m and xx x XY, which is a between input x(n) and output y(n) h. is impulse response x hm

9 33. For the active network shown in Figure, the value of V/I is R 4 I V R 6 I.4 (C) 3.6 (C) Since it is a dead network with dependent source to find V/I we have to connect an external source and measure it writing nodal equation at node A I V I A R 4 V 3.6 I V Ri 6 I 34. In a discrete-time Low pass Filter, the frequency response is A periodic A periodic with response restricted to, (C) Periodic with period Quasi periodic with response extending to infinity (C) c c 35. For the R-L circuit shown, the current i(t) for unit step input voltage will rise to.63 in s s (C).5s.5s Vi t i H t * I S SS S S

10 i t e u t t.63.5 e.6 e t t t e.6 No value of t will satisfy this equation 36. In the circuit the value of i x is i x V 3A ix A.6A (C).6A.4A Writing nodal equation A VA 3 i VA andix V i A Solving equation () and () i x =.4A and V A = 7.V x x 37. When the frequency of the applied voltage (sine wave) across an inductor is increased then the current will Decrease Increase (C) Remain same Be zero VL IL j L IL So when frequency increase current will decreases 38. A series resonant circuit is tuned to MHz and provides 3-dB bandwidth of khz. The quality factor Q of the circuit is 3 (C) (C)

11 IES PREVIOUS YEAR SOLVED QUESTION PAPERS ELECTRONICS AND COMMUNICATION ENGINEERING - 5 Publisher : Faculty Notes Author : Panel of Experts Type the URL : Get this ebook