BHEL Electrical Written Test: Questions
1.Consider the following expressions indicating the step or impulse response of an initiallyrelaxed control system-
a) (5 4e-2+) u(t)
b) (e-2t +5) (u(t))
c) V(t) + 8e-2t u(t)
d) V(t) + 4e-2t 4(t)
2.Which is the following relate to rational transfer function of a system-
a) Ratio of Fourier transform of output to input with zero initial conditions.
b) Ratio of Laplace transform of output to input with zero initial conditions.
c) Laplace transform of system impulse response.
3. Laplace transform of system unit step response select the correct answer using the codesgiven below. Codesa.)
a) 1 and 4
b) 2 and 3
c) 1 and 3
d) 2 and 4
4. For the signal g (t) 10 cos (50 pt) cos2 (150at) The Nyquist sampling state in t seconds is
a) 150 samples per second
b) 200 samples per second
c) 300 samples per second
d) 350 samples per second
5.In the case of a 70 MHz 1F carries for a transponder band width of 36 MHz; energy mustlie between MHz.
a) 34 and 106
b) 52. And 88
c) 106 and 142
d) 34 and 142
6.Radar used to eliminate clutter in navigational application is
a.) Pulse radar
b.) Tracking radar
c.) MTI radar
d.) Mono pulse radar
7.The 1.55 mm windows is not yet in use with fiber optic systems because
a.) The attenuation is higher than at 0.85 mm
b) The attenuation is higher than at 1.3mm
c.) Suitable laser devices have not yet been developed
d.) It does not lend itself to wavelength multiplexing
8.Pre-emphasis in FM systems involves-
a.) Compression of the modulating signal
b.) Expansion of the modulating signal
c.) Amplification of lower frequency components of the modulating signal.
d.) Amplification of higher frequency components of the modulating signal.
9.In a terrestrial microwave system transmission of signals is achieved through-
a.) reflection from the ionosphere
b.) line of sight mode
c) reflection from the ground
d.) diffraction from the stratosphere.
10.Casse grain feed is used with a parabolic reflector to
a.) increase the gain of the system
b) increase the bandwidth of the system
c.) reduce the size of the main reflector
d.) allow the feed to be placed at a convenient point.
11.In most microwave communication link rain drop attenuation is caused due to-
a) scattering of microwaves by water drops of specific size.
b) scattering of microwaves by a collection of droplets acing as a single body.
c) absorption of microwaves by water and consequent heating of the liquid
d) absorption of the microwaves by water vapor in the atmosphere.
12.When a (75 j40)W load is connected to a coaxial line of Z0 = 75 W at 6MHz then theload matching on the line can be accomplished by connecting-
a.) A short circuited stub at the load
b.)An inductance at the load
c.)A short circuited stub at a specific distance from the load
d.)none of the above
13.As compared to analog multimeters, digital Multimeters,s are
a.) less accurate
b.) more accurate
c.) equally accurate
14.When a signal of 10 mV at 75 MHz is to be measured then which of the followinginstruments can be used
b.) Cathode ray oscilloscope
c.) Moving iron voltmeter
d.) Digital multimeter
15.Amplifier of class B has high theoretical efficiency of 78.5 percent because-
a.) It is biased almost to saturation
b.)Its quiescent current is low
c.)Its output is an exact replica of its input
d.)It is biased well below cut off
16.The coupling that produces minimum interference with frequency response is-
a.) Direct coupling
b.) Impedance coupling
c.) R C coupling
d.) Transformer coupling
17.A superconductor is a
a.) A material showing perfect conductivity and Meissner effect below a critical temperature
b.) A conductor having zero resistance
c.) A perfect conductor with highest di-magnetic susceptibility
d.) A perfect conductor which becomes resistance when the current density through itexceeds a critical value
18.When an inductor tunes at 200 KHz with 624 pF capacitor and at 600 KHz with 60.4 pFcapacitor then the self capacitance of the inductor would be
a) 8.05 pF
19.The Q of a radio coil
a) is independent of frequency
b) increases monotonically as frequency increases
c) decreases monotonically as frequency increases
d) increases upto a certain frequency and then decreases beyond that frequency
20.When a generator of internal impedance and operating at 1GHz feeds a load via a coaxialline of characteristic impedance 50 ohm then the voltage wave ratio on the feed line is -
21.The coding system typically used in digital telemetry is
a.) PPM (pulse position modulation)
b.) PAM (pulse amplitude modulation)
c.) PCM (pulse code modulation)
d.) PDM (pulse duration modulation)
22.Radiation pyrometers are used for the measurement of temperature in the range of
a.) -2000C to 5000C
b.) 00C to 5000C
c.) 5000C to 12000C
d.) 12000C to 25000C
23.RF amplifier of an A.M. receiver is normally biased in
a.) Class ,A,
b.) Class ,b,
c.) Class ,C,
24.The value of gate voltage for the operation of enhancement of only N channel MOSFEThas to be
a.) High positive
b.) High negative
c.) Low positive
26. A centrifugal pump has speed-1000rpm, Flow-1200l.p.m, Head-20m, Power-5H.P. If itsspeed is increased to 1500rpm, new flow will be.: = 1800l.p.m
27. Runaway speed of a hydraulic turbine is: = the speed if the turbine runner is allowed torevolve freely without load and with the wicket gates wide open.
28. 10m of water column is equal to = 100kN/m2
29. M.I. of a circular area about an axis perpendicular to the area is: = pr4/2
30. A projectile is fired at an angle ? to the vertical. Its horizontal range will be maximumwhen ? is . =45
31. An elevator weighing 1000kg attains an upward velocity of 4m/sec in two seconds withuniform acceleration. The tension in the supporting cables will be = 1200kg.
32. A 13m ladder is placed against a smooth vertical wall with its lower end 5m from thewall. What should be the co-efficient of friction between ladder and floor so that it remains inequilibrium. = 0.21
33. A car is moving with a velocity of 60km/hr and possesses energy of 5105 joules. Themass of the car will be. =3000kg.
34. If l is the span of a light suspension bridge whose each cable carries total weight (w) andthe central diop is y, the horizontal pull at each support is: = wl/y OR
35. A beam of length l, having uniform load w kg/unit length is supported freely at the ends.The moments at mid span will be: = wl2/8.
36. A boiler shell 200cm dia and plate thickness 1.5cm is subjected to internal pressure of 1.5MN/m2, then the hoop stress will be. = 100N/m2
37. 100KW is to be transmitted by each of two separate shafts. A is turning at 250rpm and Bat 300rpm. Which shaft must have greater diameter.: = B
38. Two identical leaf springs of spring constant k are arranged like cantilevers in parallel andattached at free end by a spring of spring constant k. The equivalent spring constant of combination is; = 1.5k.
39. Automobile steering gear is an example of: = lower pair.
40. The type of coupling used to join two shafts whose axes are neither in same straight linenor parallel, but intersect is. = Universal coupling.
41. To transmit power from one rotation shaft to another whose axes are neither parallel norintersecting, use: = Spiral gear.
42. A gear having 100 teeth is fixed and another gear having 25 teeth revolves around it, thecentre lines of both gears being joined by an arm. How many revolutions will be made bygear of 25 teeth for one revolution of arm. = 5 rev.
43. The secondary critical speed of a shaft occurs at: = twice the speed of primary criticalspeed.
44. Brittle coating technique is used for: = experimental stress analysis.
45. Factor of safety is the ratio of: = yield stress/working stress.
46. Type of gear used for non-intersection perpendicular shafts: = Hypoid gears.
47. Corrosion resistance of steel is increased by adding: = Chromium & Nickel
48. The product of Cupola is called: = cast iron49. Brinell tester uses a hardness steel ball of size: = 10mm