PSU Sample Paper 7


1.         When compared to a first-order low-pass filter, a second order low-pass filter has
            A. lower voltage gain
            B. higher voltage gain
            C. faster drop in filter response
            D. higher cut-off frequency.
2.         Three concentric conducting spherical surfaces of radii R1, R2 and R3 (R1< R2< R3) carry charges of -1, -2 and 4 coulombs respectively. The charges on the inner and outer surfaces of the outermost sphere will be respectively (in coulombs).
            A. 0, 4
            B. 3, 1
            C. -3, 7
            D. -2, 6
3.         In a power MOSFET switching times are of the order of few
            A. seconds
            B. milliseconds
            C. microseconds
            D. nano seconds.

4.         VTVMs have
            A. very high ohms / volt rating
            B. moderate ohms / volt rating
            C. low ohms / volt rating
            D. very low ohms / volt rating
5.         The characteristic equation of a closed-loop system is given by
                        s4 + 6s3 + 11s2 + 6s + K = 0
            Stable closed loop behavior can be ensured when gain K is such that

  • 0 < K < 10
  • K > 10
  • – µ£ K <µ
  • 0 < K £ 20

6.         The disk head is initially at sector 0, track 0. If all three files A, B and C are to be read in the minimum amount of time, they should be read in the following order :
            A. A, B, C
            B. A, C, B
            C. B, A, C
            D. B, C, A.
7.         If 8 identical RC sections are used in the feedback path of a phase-shift oscillator (with non-inverting amplifier) it will oscillate at the frequency at which each section shifts phase by
            A. 30º
            B. 45º
            C. 60º
            D. 22.5º
8.         A discrete zero memory information source has 40 symbols is equally likely. The minimum number of bits required to code the source with uniform length code and the entropy of the source are respectively
            A. 5, 5.03
            B. 6, 5.83
            C. 5, 6.64
            D. 6, 5.32
9.         Which of the following is an example of a spooled device ?
            A. a line printer used to print the output of a number of jobs
            B. a terminal used to enter input data to a running program
            C. a secondary storage device in a virtual memory system
            D. a graphic display device.
10.       Which of the following devices does not have negative resistance characteristics?
            A. UJT
            B. Tunnel diode
            C. SCR
            D. FET
11.       Silicon steel is widely used in
            A. cutting tools
            B. dies and punches
            C. electrical industry
            D. chemical industry.
12.       When there is a snowy picture, the trouble lies in
            A. R.F. amplifier
            B. antenna
            C. too much AGC
            D. weak vertical amplifier.
13.       A solution of the blind speed problem is to
            A. change to Doppler frequency
            B. vary the PRF
            C. use monopulse
            D. use MTI.
14.       A magnetron whose oscillation frequency is electrically adjustable over a wide range is called as
            A. frequency agile magnetron
            B. VTM
            C. coaxial magnetron
            D. none of the above.
15.       No picture, no sound, no raster, trouble is in
            A. vertical oscillator
            B. R.F. amplifier
            C. horizontal amplifier
            D. Video amplifier.

16.       A periodic rectangular signal, x(t) has the waveform shown in Figure below. Frequency of the fifth harmonic of its spectrum is

  • 40 Hz
  • 200 Hz
  • 250 Hz
  • 1250 Hz

17.       The potential difference between the forces A and B of a uniformly polarized infinite slab shown in the figure is :

18.       Which type of power supply is usually preferred for PC ?
            A. Switched mode power supply
            B. Resonant power supply
            C. Bidirectional power supply
            D. none of the above
19.       A radio frequency (RF) probe in VTVM is used to measure
            A. high resistances
            B. low frequency voltages
            C. high frequency voltages
            D. low resistances
20.       By a suitable choice of the scalar parameter K, the system shown in the figure given below, can be made to oscillate continuously at a frequency of

  • 1 rad / s
  • 2 rad / s
  • 4 rad / s
  • 8 rad / s

21.       The disk head is initially at sector 0, track o. If all three files A, B and C are to be read in the minimum amount of time, they should be read in the following order :
            A. 143.9 ms.
            B. 116.4 ms.
            C. 114.0 ms.
            D. 102.6 ms.
22.       In the circuit shown in figure |V0| = 1 V for a certain set of values of w, R and C. |V0| will remain as V even if

  • w is doubled
  • w is halved
  • R is halved
  • C is doubled.

23.       The information capacity (bits / sec.) of a channel with bandwidth W and transmission time T is given by
            A. C µ WT
            B. C = W / T
            C. C = T / W
            D. C = W2 T
24.       A ROM is used to store the table for multiplication of two 8-bit unsigned integers. The size of ROM required is
            A. 256 × 16
            B. 64 K × 8
            C. 4 K × 16
            D. 64 K × 16
25.       Araldite is
            A. vegetable oil resins
            B. thermosetting plastic
            C. epoxy resin
            D. a variety of PVC.
26.       Bakelite is a
            A. acrylate
            B. silicon varnish
            C. thermoplastic synthetic resin
            D. phenol formaldehyde resin.
27.       The shadow mask in a colour picture tube is use to
            A. reduce X-ray transmission
            B. increase screen brightness
            C. ensure that each beam hits only its own dots
            D. none of these.
28.       Blind speed causes target appear
            A. Moving
            B. Stationary
            C. Distinguish correctly
            D. none of the above
29.       To overcome difficulties with strapping high frequencies the type of cavity structure desired for magnetron is
            A. hole and slot
            B. slot
            C. rising run
            D. vane.
30.       The function of telegraph repeater is
            A. to repeat the signal
            B. to amplify the signal
            C. to amplify the signal and eliminate distortion in the signal
            D. demodulate the signal.

31.       In the circuit shown in figure below, X is an element which always absorbs power. During a particular operation, it sets up a current of 1 amp in the direction shown and absorbs a power Px. It is possible that X can absorb the same power Px for another current i; the value of this currents is

  • amps.
  •  amps
  • 5 amps
  • None of the above.

            The electric field across an interface is shown in the fig. The surface charge density
            (in coulombs / m2) on the interface is

  • -4 Î0
  • -3Î0
  • + 3 Î0
  • + 4Î0

33.       Which of the following statements are correct ?
            1.         BJTs have positive temperature coefficient
            2.         Diodes are connected in series to increase the blocking voltage capability
            3.         The input power factor of controllers,
which varies with delay angle, is generally poor, especially at the low output range

  • 1 and 2 only
  • 2 and 3 only
  • 1 and 3 only
  • 1, 2 and 3

34.       The best method of measuring capacitance is the
            A. C.R.O. method
            B. VTVM method
            C. Voltmeter-ammeter method
            D. a.c. bridge method.
35.       The open-loop transfer functions with unity feedback are given below for different systems :
            Among these systems, the unstable system is

  • 1
  • 2
  • 3
  • 4

36.       The most nearly average latency time is
            A. 1 ms.
            B. 7 ms.
            C. 30 ms.
            D. 50 ms.
37.       Figure shows the circuit diagram of a Wien bridge oscillator using the op-amp. The frequency of oscillation is given by f = 1 / 2p CR. To have the system oscillate the ratio R2 / R1 should be

  • 0.5
  • 29
  • 2
  • Any value

38.       If each stage had a gain of 10 dB, and noise figure of 10 dB, then the overall noise figure of a two-stage cascade amplifier will be
            A. 10
            B. 1.09

C. 1.0
            D. 10.9
39.       Number of machine cycles required for RET instruction in 8085 microprocessor is
            A. 1
            B. 2
            C. 3
            D. 5
40.       Bakelite is a
            A. phenol formaldehyde resin
            B. acrylate
            C. thermoplastic synthetic resin
            D. silicon varnish.
41.       Which of the following is a copper free allowy ?
            A. Brass
            B. Phosphor bronze
            C. Invar
            D. Muntz metal.
42.       In TV system function of equalizing pulses is
            A. to smooth out differences between the vertical sync signals
            B. to maintain horizontal synchronization over three line periods
            C. to smooth out difference between horizontal sync signals.
            D. none of the above.
43.       Indicate which one of the following application or advantages of radar becomes false
            A. Target identification
            B. Navigation
            C. Very significant extension of the maximum range
            D. More accurate tracking of enemy target.
44.       TWT is characterized by
            A. low noise figure wide bandwidth and average gain
            B. gain exceeding 40 dBs, wide bandwidth and low noise figure
            C. more noise and wide bandwidth
            D. none of the above
45.       Linear velocity of a satellite equals



1.C.     The filter has faster drop in filter response.
The total charge on spheres 1 and 2 taken together is -1 + (-2) = -3C. This charge will induced + 3C on inner surface and -3C on the outer surface of sphere 3. Thus the total charge on the inner surface of sphere 3 is 3C and on the outer surface -3 + 4 = 1C.
3.D.     In case of power MOSFETs the switching speed is very high and the switching times are of the order of nano seconds.
4.A.     VTVMs have very high ohms / volt rating.
5.A.     s4                     1                      11                    K
            s3                     6                      6                      –
            s2                     10                    K                     –
            s1                6 – 0.6 K               –                       –
            s0                     K                     –                       –
                        \ K ³ 0 and also 6 (1 – 0. 1K) ³ 0
            Thus, 0 £ K £ 10.
6.B.     Latency time is the time required to rotate the disk of the proper sector and seek time is the time required to move the disk head to the proper track. It takes 200 ms to rotate the disk through 20 sectors, i.e., 10 ms per sector. It takes 20 ms to rotate the disk through 10 tracks, i.e. 2 ms per track.
                        Traversing five tracks equals traversing one sector. Therefore, try to minimize the number of sectors traversed. Reading A then C then B means going from sectors 0 to 1 to 3 to 5, a total of 5 sectors are traversed, and from tracks 0 to 6 to 5 to 2, a total of 10 tracks are traversed. Any other order would require traversing atleast two additional sectors and atleast six tracks.
7.B.     For a non-inverting amplifier, phase shift required is 360º.
                        For 8 sections,
            phase shift / phase
8.D.     H = S Pu log2 1 / Pu = log2 40 = 5.32
9.A.     A line Printer.
10.D.   FET device does not have negative resistance characteristics.
11.C.   Silicon steel is widely used in electrical industry for motor stampings and transformer cores.
12.A.   When there is a snowy picture, the trouble lies in R.F. amplifier.
13.B.   A solution of the blind speed problem is to vary the PRF.
14.B.   The wide range is called as VTM.
15.C.   Horizontal amplifier has no trouble in picture, sound and raster.

16.D.   The signal shown has time period T = 4 ms. Therefore, f = 1 × 103 / 4 = 250 Hz. This is the fundamental frequency. Fifth harmonic frequency, f5 = 250 × 5 = 1250 Hz.
17.A.   D = Î0 E + P; D = Î0Îr E
            \Î0Îr E = Î0 E + P or E =  
            \ Potential difference V = Ed =  
18.A.   Switch mode power supply.
19.C.   A radio frequency probe in VTVM is used to measure high frequency voltages.
20.C.   For a system with feedback loop to oscillate ab = -1, where a = G(s) and b = Feedback path gain or alternatively, the ch. eqn. is solved.
            or s(s + 2) (s + 8) + k = 0
            Thus, the same is the ch. eqn.
               1 + G (s) H (s) = 0.
               8 (s2 + 10s + 16) + K = 0
            jw (-w2 + 10jw + 16) + K = 0
            For this system to oscillate j terms should be set to zero.
            \  – jw3 + 16 jw = 0 or w = 4 rad / s.
            And then, – 10 w2 + k = 0 or K = 160.
21.B.   Read C : traverse 3 sectors, 5 tracks, read 2 blocks
            Read B : traverse 2 sectors, 3 tracks, fead 5 blocks.
            Read A : traverse 4 sectors, 4 tracks, read 1 block.
            Total : traverse 9, sectors-12, tracks 8 blocks
            Total time to read = 9 × 10 + 12 × 2 + 8 × 0.3
                                         = 116.4 ms.
22.A.   Please refer to all pass filter circuit
            So when w, R and C are changed by the same magnitude, the TF is unchanged at 1.
            Answers (b), (c) and (d) are also correct.
23.D.   If is W2T = (1./ sec2). Sec = 1 / sec.
24.D.   64 K × 16
25.C.   Araldite is an epoxy resin
26.D.   Phenol formaldehyde resin.
27.A.   It used to ensure that each beam hits only its own dots.
28.B.   Blind speed causes target appear stationary.
29.C.   It is raising sun.
30.C.   The function of telegraph repeater is to amplify the signal and eliminate distortion in the signal. 
31.C.   For the conditions shown, the current is 1A and the voltage across X is 5V. Therefore, the power is 5W. If the current is 5A, then the voltage across X becomes 6 – 5 × 1 = 1V and the power absorbed by it is 1 × 5 = 5W.
32.A.   the boundary condition for displacement density D is in. (D1 – D2) = rs where in is the unit normal vector directed from medium 2 to medium 1, and rs is the surface charge density at the interface. It is specified here that E1 and E2 are entirely normal to the interface, assuming to ax to be a unit normal vector.
            D1 = 2 × 1 e0 in ;
            D2 = 3 × 2 e0 in
            \ in (2 in – 6 in) e0 = -4 e0 
            thus, rs = – 4Î0.
33.B.   BJTs have a negative temperature coefficient.
34.D.   A.C. Bridge is the best method of measuring capacitance.
35.C.   If G(s) = N(s) / D(s), then with unity feedback loop ch. eqn. is N(s) + D(s) = 0. For the system to be stable, the roots of ch. eqn. should neither lie in RHP, nor it should have multiple poles on the imaginary axis.
                        It can be quickly checked that the real parts of roots of check quotations for 1, 2 and 4 are negative. To find the roots or s2(s + 2) + 2 = 0 is slightly difficult. However, one concludes without actually checking that answer is (c).
36.D.   Regardless of initial sector, we can arrive at the destination sector by rotating the disk through atleast zero both directions. Therefore, we must traverse about 5 sectors on the average. Thus, the most likely average latency time is 5 × 10 ms = 50 ms.
37.A.   The negative feedback should be such as to give gain of 3 and above
38.D.   F = F1 + (F – 1 / ga1) = 10 + 9 / 10 = 10.9
39.C.   3 machine cycles
40.A.   Bakelite is a phenol formaldehyde resin.
41.C.   Invar is nickel (36%) iron (64%) alloy. Standard brass contains 70% copper and 30% zinc. Phosphor bronze contains 90% copper, 0.7 tin and 0.3 phosphorous. Muntz metal contains 60% copper, 40% zinc.
42.A.   In TV system function of equalizing pulses is to smooth out differences between the vertical sync signals.
43.D.   More accurate tracking of enemy target.
44.B.   TWT is characterized by gain exceeding 40 dBs wide bandwidth and average gain.
45.B.   Linear velocity of a satellite equals