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Thursday, March 17, 2011

Electronics engineering Questions

Electronics Engineering Questions For SAIL, GAIL, ONGC, IES & Other Exams

1.Consider two samples of silicon semiconductor identical in all respects except that one is uniformly doped with1015 cm10-3 donor impurity atoms (Sample A) and the other is non-uniformly doped with donors from one side such that Nd(x) = N0 e -ax (sample B). Let a = 1 hm-1 and N0= 1017 cm-3 . Consider the following sample B.
1. Sample A will not have any current at equilibrium but current will flow out of sample B
2. Both samples will have built-in electric, field
3. Sample A will have zero built-in electric field whereas sample B will have a constant built-in electric field
4. No current will flow at equilibrium from either sample A or sample B
Select the correct answer using the codes given below:
(a)1 and 2
(b) 1 and 3
(c) 1 and 4
(d) 3 and 4

2. Consider the following statements:
The temperature dependence of resistivity of a sample of N-type silicon is based upon carrier concentration and carrier mobility variations with temperature
1. the resistivity of silicon increases with temperature.
2. the mobility decreases with temperature
3. the carrier concentration increases with temperature
4. the resistivity of silicon decreases with temperature
Which of these statements are correct?
(b) 2,3and
(c)1 and2
(d) 3and 4
3. The unit of mobility is
(b) mV-1s-1
(d) Vms-1
4. The Haynes-Shockley experiment enables one to determine the
(a) diffusion coefficient of majority carriers
(b) effective mass of the minority carriers
(c) mobility of the minority carriers
(d) lifetime of the majority carriers
5. The Hall constant in p-Si bar is given by 5 x 103 cm35/Coloumb The hole concentration in the bar is given by
(a) 1.00 x 1015/ cm3
(b) 1.25 x 1015/ cm3
(c) 1.50 x 1015/ cm3
(d) 1.60 x 1015/ cm3 -
6. In an extrinsic semiconductor, the Hall coefficient RH
(a) increases with increase of temperature
(b) decreases with increase of temperature
(c) is independent of the change of temperature
(d) changes with the change of magnetic field
7. Consider a semiconductor bar having square cross-section. Assume that holes drift in the positive x-direction and a magnetic field is applied perpendicular to the direction in which holes drift. The sample will show
(a) a negative resistance in positive y-direction
(b) a positive voltage in positive y-direction
(c) a negative voltage in positive y-direction
(d) a magnetic field in positive y-direction
8. The change in barrier potential of a silicon p-n junction with temperature is
(a)0.025 Volts per degree C
(b) 0.250 Volts per degree C
(c)0.030 Volts per degree C
(d) 0.014 Volts per degree C
9.Moor’s law relates to
(a) speed of operation of bipolar devices
(b) speed of operation of MOS devices
(ç) power rating of MOS devices
(d) level of integration of MOS devices
10. The colour T. V. picture signal is a
(a) single-channel, one-dimensional signal
(b) single-channel, three-dimensional signal
(c) three-channel, one-dimensional signal
(d)three-channel, three-dimensional signal
11 Consider the following statements:
1. Fourier transform is special case of Laplace transform.
2. Region of convergence need not be specified for Fourier transform.
3. Laplace transform is not unique unless the region of convergence is specified.
4. Laplace transform is a special case of Fourier transform.
Which of these statements are correct?
(a)2 and 4
(b) 4 and 1
(c)4, 3 and 2
(d) 1, 2 and 3
12. The units of the spectrum obtained by Fourier transforming the covariance function of a stationary stochastic process is?
(a)power per Hertz
(b) energy per Hertz
(c)power per second
(d) energy per second
13. The maximum power that a 12 V d.c. source with an internal resistance of 20 Ohms can supply to a resistive load is ?
(b) 18W
(d) 48W
14. Consider the following statements associated with the Superposition theorem:
1. It is applicable to d.c. circuits only.
2. It can be used to determine the current in a branch or voltage across a branch.
3. It is applicable to networks consisting of more than one source.
4. It is applicable to networks consisting of linear and bilateral elements.
Which of these statements are correct?
(a)1, 2 and 3
(b) 2, 3 and 4
(c)3, 4 and 1
(d) 4, 1 and 2
15. Which one of the following statements is NOT a property of R-L driving point
(a) The first critical frequency at the origin is a zero
(b) The last critical frequency is a pole
(c) The impedance at S =infinity is always less than the impedance at S = zero
(d) The slope of the impedance curve is positive at all points
16. In a network containing resistances and reactances the roots of the characteristic
equation give for the circuit
(a)the forced response
(b) the total response
(c)the natural response
(d) the damped response
17. Consider the following:
Energy storage capability of basic passive elements is due to the fact that
1. resistance dissipates energy
2. capacitance stores energy
3. inductance dissipates energy
Which of the above is/are correct?
(a)1, 2 and 3
(b) 1 and 3
(c) 3 alone
(d) 1 and 2
18. √L/C has the dimension of
(b) capacitance
(d) resistance
19. A network N’ is dual of network N if
(a) both them have same mesh equations
(5) both of them have the same node equations
(c) mesh equations of one are the node equations of the other
(d) KCL and KVL equations are the same
20. The input impedance of a short circuited quarter wave long transmission line is
(a) purely reactive
(b) purely resistive
(c) dependent on the characteristic impedance of the line
(d) none of the above
21. For a wave propagating in an air filled rectangular waveguide
(a) guided wavelength is never less than the free space wavelength
(b) wave impedance is never less than the free space impedance
(c) TEM mode is possible if the dimensions of the waveguide are properly chosen
(d) Propagation constant is always a real quantity
22. Consider the following statements with reference to Brewster angle:
1. For oblique incidence at a boundary, there is no reflected wave when the incident wave is vertically polarized.
2. Brewster angle can occur only at the boundary of a perfect conductor.
3. For a horizontally polarized wave, there is no Brewster angle.
4. When the incident wave is not fully vertically polarized, there will be a reflected component which is horizontally polarized.
Which of these statements are correct?
(b) 2,3and4
(c)3, 4 and 1
(d) 4, 1 and 2
23. When a particular mode is excited in a wave-guide, there appears an extra electric component in the direction of propagation. The resulting mode is
(a) transverse-electric
(b) transverse-magnetic
(c) longitudinal
(d) transverse-electromagnetic
24. The most suitable primary standard for frequency is
(a)Rubidium vapour standard
(b) Quartz standard
(c)Hydrogen maser standard
(d) Caesium beam standard
25. Horizontally mounted moving iron instruments employ
(a)Eddy current damping
(b) Air friction damping
(c)Fluid friction damping
(d) Electromagnetic damping
26. There are four types of controlled sources, namely VC VS, VC CS, CC CS, CC VS.
It is required to select a proper controlled source configuration for interfacing
the output of a high-impedance microphone to a low impedance loudspeaker.
The proper source will be
(a) VC VS (Voltage Controlled Voltage source)
(b) VC CS (Voltage Controlled Current Source)
(c) CC CS (Current Controlled Voltage Source)
(d) CC VS (Current Controlled Voltage Source)
27. Some of the functional building blocks of a measurement system are:
Primary Sensing Element (PSE)
Variable Conservation Element (VCE),or Transducer
Data Transmission Element (DTE)
Variable Manipulation Element (VME)
Data Presentation Element (DPE)
The correct sequntial connection of the functional building blocks for an
electronic pressure gauge will be
28. According to Guassian statistical analysis, if the confidence level is 0.80, then the values lying outside the confidence interval are
(a)1 in 5
(b) 1 in 10
(c)1 in 20
(d) 8 in 10
29. The true rams. voltmeter employs two thermocouples in order to
(a) prevent drift
(b) increase the accuracy
(c) increase the sensitivity
(d) cancel out the nonlinear effects of first thermocouple
30. A certain oscilloscope with 4cm by 4cm screen has its own sweep output fed to its input. If the x and y sensitivities are same, the oscilloscope will display a
(a) saw-tooth wave
(b) triangle wave
(c)diagonal line
(d) horizontal line
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