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Multiple choice question for engineering

Set 1

1. The members of the antenna family which are made of wires of certain value in terms of operating wavelength are called:
a) Loop antennas
b) Wire antennas
c) Dipole antenna
d) Slot antennas

View Answer

Answer: c [Reason:] Wires of half wavelength are termed as dipoles. Their radiation resistance is about 73 Ω. If only half of this length is used, then it is called quarter-wave monopole with a radiation resistance of 36.5 Ω.

2. The antenna in which location of the feed determines the direction of the lobe are:
a) Wire antenna
b) Loop antenna
c) Helical antenna
d) Horn antenna

View Answer

Answer: a [Reason:] In a wire antenna, the location of the feed determines the direction of the lobe and the orientation of the wire determines the polarization. These wires can be thick or thin. Thickness of the wire determines the radiation resistance of the antenna.

3. Based on the size of the loops, loop antennas are classified as small and large loops. This is the only classification of loop antenna.
a) True
b) False

View Answer

Answer: b [Reason:] Loop antennas are classified based on various antenna parameters. To name a few, small and large loops, circular and square loops, loops having single or multi turns, loops with turns wound using a single wire or multiple wires.

4. Antenna that does not belong to the horn antenna family among the following are:
a) Pyramidal horn
b) Conical horn
c) bi-conical horn
d) None of the mentioned

View Answer

Answer: d [Reason:] All of the above mentioned antennas belong to the horn antenna family. Horn antennas may be made of pointed or rounded waveguides. The waveguides may contain disc at an end or some dielectric.

5. Patch antennas are the antennas of small size and are made of:
a) Strip line
b) Microstrip lines
c) Coaxial cables
d) Rectangular waveguide

View Answer

Answer: b [Reason:] Patch antennas are microstrip antennas that can be of any shape. Patch antennas can be aperture-coupled fed or proximity fed. For obtaining circular polarization, a patch may also be doubly fed.

6. Reflector antennas are widely used to modify radiation patterns of radiating elements.
a) True
b) False

View Answer

Answer: a [Reason:] Reflector antennas are used to modify radiation patterns of radiating elements. Reflector antennas are classified into two categories. They are passive reflectors and active reflectors. Based on the type of the radiating element and the modification in the radiation pattern required, accordingly either active or passive reflectors are chosen.

7. The pattern of the reflector in a reflector antenna is called:
a) Primary pattern
b) Secondary pattern
c) Reflector pattern
d) None of the mentioned

View Answer

Answer: b [Reason:] In a reflector antenna, the feed pattern is called primary pattern and the pattern of the reflector is called secondary pattern. These antennas are widely employed in RADARs and other types of point to point communication links.

8. ______ antennas have gain less than reflector antennas but have more lenient tolerance on surfaces.
a) Helical antennas
b) Lens antennas
c) Array antennas
d) Slot antennas

View Answer

Answer: b [Reason:] Lens antennas are complex in nature but are able to scale wider angles. In comparison to reflectors, their gain is 1 or 2 dB less, but these have more lenient tolerance on surfaces. These have less rearward reflection, relatively low loss and can be easily shaped to the desired contours.

9. Lens antennas are classified into two types. One being fast antenna, the other one is:
a) Slow antenna
b) Delay antenna
c) Dynamic antenna
d) None of the mentioned

View Answer

Answer: b [Reason:] In delay lenses, the electrical path length is increased or the wave is retarded by the lens medium. Dielectric lenses and H-plane metal lenses fall in this category.

10. The antennas which offer high operational bandwidth and the antenna parameters are maintained over a wide range of antennas are called:
a) Wide band antennas
b) Array antennas
c) Parabolic antennas
d) None of the mentioned

View Answer

Answer: a [Reason:] In this class of antennas, constancy of impedance and radiation characteristics is maintained over a wide range of frequencies. To be wide band or frequency independent, antennas should expand or contract in proportion to the wavelength.

11. High directivity required in RADAR communication is satisfied using this type of antennas:
a) Wide band antennas
b) Antenna arrays
c) Slot antennas
d) Patch antennas

View Answer

Answer: b [Reason:] Higher directivity is the requirement in point to point communication. This can be achieved by increasing the size of the antennas in terms of electrical length. When much high directivity is required, antenna arrays are used.

12. The terminal impedance of a dipole antenna is 710 Ω. The terminal impedance of the slot antenna given the intrinsic impedance of air is 377 Ω is:
a) 100 Ω
b) 50 Ω
c) 25 Ω
d) None of the mentioned

View Answer

Answer: b [Reason:] The terminal impedance ZS of the slot is given by the relation Z02/ 4Zd) Zₒ is the intrinsic impedance of the medium and ZD is the terminal impedance of the dipole. Substituting the given values in the above equation, the terminal impedance of sot is 50 Ω.

13. If the length of aperture in a pyramidal horn antenna is 10cm and δ for the design is 0.25. Then, the flaring angle of the pyramidal horn is:
a) 30⁰
b) 25.4⁰
c) 45⁰
d) 60⁰

View Answer

Answer: b [Reason:] The flaring angle of pyramidal horn is given by 2cos-1(L/L+δ). Substituting the values of L and δ, flaring angle is 25.4⁰.

14. If the directivity of a square corner receiving antenna is 20 and operating at a wavelength of 0.25m, the effective aperture of a square corner antenna is:
a) 0.4 m2
b) 0.2 m2
c) 0.1 m2
d) None of the mentioned

View Answer

Answer: a [Reason:] Given the directivity of the antenna, effective aperture of the antenna is given by Dλ2/4π. substituting the given values of the variables; the effective aperture of the antenna is 0.4 m2.

Set 2

1. An antenna source that radiates energy uniformly in all the directions is called:
a) Isotropic source
b) Anisotropic source
c) Point source
d) None of the mentioned

View Answer

Answer: a [Reason:] Isotropic source radiates energy in all the direction uniformly. For such a source, the radial component Sr of the pointing vector is independent of θ and φ. The three dimensional power pattern of n isotropic source is a sphere.

2. Antennas that radiate energy only in a specified are called anisotropic antennas.
a) True
b) False

View Answer

Answer: a [Reason:] All physically realizable, simplest antennas also have directional properties. That is, they radiate energy in one direction than in any other direction. Such sources are called anisotropic point sources.

3. The expression for pointing vector of an isotropic point source at a distance ‘r’ from the source is given by:
a) P/ 4πR2
b) P/4π
c) P/ 4πR
d) P×4πR2

View Answer

Answer: a [Reason:] The pointing field vector for an isotropic source is given by the expression P/ 4πR2.P is the total power radiated y the source. As the distance of the point from the source increases, the magnitude of pointing vector decreases.

4. A source has a cosine radiation-intensity pattern given by U=UM cos (θ). The directivity of this source is:
a) 2
b) 4
c) 6
d) 8

View Answer

Answer: b [Reason:] To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 4.

5. A source has a cosine power pattern that is bidirectional. Given that the directivity of a unidirectional source with cosine power pattern has a directivity of 4, then the directivity of the unidirectional source is:
a) 1
b) 2
c) 4
d) 8

View Answer

Answer: b [Reason:] Given the directivity of unidirectional power pattern, the directivity of bidirectional power pattern is half of it. Hence the directivity of the source is 2.

6. A source has a radiation intensity pattern given by U=UM sin θ. The directivity of the source with this power pattern is:
a) 1
b) 1.27
c) 2.4
d) 3.4

View Answer

Answer: b [Reason:] To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 1.27.

7. A source has a sine squared radiation intensity power pattern. The directivity of the given source is:
a) 1.5
b) 3
c) 2.5
d) 3.5

View Answer

Answer: a [Reason:] To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 1.5.

8. A source with a unidirectional cosine squared radiation intensity pattern is given by UMcos2 (θ). The directivity of the given source is:
a) 6
b) 8
c) 2
d) 7

View Answer

Answer: a [Reason:] To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by anisotropic source gives the directivity. Following the above steps, the directivity of the given source is 6.

9. Considering distance as a parameter, two types of field zones can be defined around an antenna.
a) True
b) False

View Answer

Answer: a [Reason:] Considering distance as a parameter, two types of field zones can be defined around an antenna) .The field near the antenna is called near field or Fresnel region and the other region is the far field that is also called as Fraunhofer region.

10. If the field strength at receiving antenna is 1 µV/m, and the effective aperture area is 0.4 m2 and the intrinsic impedance of the medium is 377 Ω, then the power received by the antenna is:
a) 1.06 pW
b) 1.06 fW
c) 2 µW
d) None of the mentioned

View Answer

Answer: b [Reason:] The received power by the antenna is given by E2Ae/Zₒ. Substituting the known values in the above equation, the power received is 1.06×10-15 watts.

Set 3

1. __________ system obtains information about a target by transmitting a signal and receiving the echo from the target.
a) Radar
b) Sonar
c) Radiometer
d) None of the mentioned

View Answer

Answer: a [Reason:] Radar stands for radio detection and ranging. A radar system obtains information about a target by transmitting a signal and receiving the echo from the target. They are also called as active remote sensing systems.

2. Radiometry is a technique or the principle on which radar works.
a) True
b) False

View Answer

Answer: b [Reason:] Radiometry is a passive technique which develops information about a target solely from the microwave portion of the blackbody radiation that it either emits directly or reflects from the surrounding bodies.

3. According to Planck’s radiation law, a body can radiate energy to the medium surrounding it under all conditions invariably.
a) True
b) False

View Answer

Answer: b [Reason:] A body in thermal equilibrium only can radiate energy according to Planck’s radiation law. The radiating body has to be maintained in thermal equilibrium. In the microwave region this reduces to P=kTB, where k is the Boltzmann’s constant.

4. A major challenge in designing a radiometer is:
a) Design complexity
b) High cost
c) Requirement of highly sensitive receivers
d) None of the mentioned

View Answer

Answer: c [Reason:] The basic problem with building a radiometer is to build a receiver that can distinguish between the desired external radiometric noise and the inherent noise of the receiver. This application thus requires that are highly efficient in detecting the required signal.

5. The receiver model of a total power radiometer is based on the:
a) AM receiver
b) FM receiver
c) Super heterodyne receiver
d) None of the mentioned

View Answer

Answer: c [Reason:] The front end of a receiver is a standard super heterodyne circuit consisting of an RF amplifier, a mixer/ local oscillator, and an IF stage. These stages are the same as that used in a super heterodyne receiver.

6. The system bandwidth of a total power radiometer is determined by the:
a) RF amplifier
b) Local oscillator
c) IF filter
d) IF amplifier

View Answer

Answer: c [Reason:] The system bandwidth of a total power radiometer is determined by the IF filter section present in the receiver circuit of the radiometer. The upper and lower cutoff frequency of the IF filter specify the system bandwidth.

7. The integrator circuit after the detector in the receiver circuit is used to smooth out the short term variations in the signal power.
a) True
b) False

View Answer

Answer: b [Reason:] The integrator used is essentially a low pass filter with a fixed cutoff frequency, and serves to smooth out short term variations in the noise power.

8. The dominant factor affecting the accuracy of the total power radiometer is the variation of ___________
a) Gain in the overall system
b) The feedback circuit
c) Efficiency of the system
d) None of the mentioned

View Answer

Answer: a [Reason:] The dominant factor affecting the accuracy of the total power radiometer is the variation of the gain of the overall system. Since such variations have relatively a longer time constant, it is possible to eliminate this error by repeatedly calibrating the device.

9. A Dicke radiometer is identical to the total power radiometer in all aspects except that they have different receiving antenna.
a) True
b) False

View Answer

Answer: b [Reason:] In a Dicke radiometer, the input is periodically switched between the antenna and a variable power noise source. This switch is called Dicke switch. Repeatedly calibrating the device is the principle behind the operation of Dicke radiometer.

10. A typical radiometer would measure the brightness temperature over the range of about:
a) 50-300 K
b) 100-200 K
c) 400-500 K
d) None of the mentioned

View Answer

Answer: a [Reason:] Typical radiometer would measure the brightness temperature over the range of about 50-300K. This then implies that the reference noise source would have to cover the same range, which is difficult to achieve practically.

Set 4

1. Which of the following is not the characteristic of ion selective electrodes?
a) It is fragile
b) Easy to use
c) Available in different sizes and shapes
d) It is insensitive to many ions

View Answer

Answer: a [Reason:] Ion selective electrode is rugged in construction. It is highly selective to a particular ion.

2. In glass membrane electrode, the glass containing 11% Na2O, 18% Al2O3, 71% SiO2 is highly sensitive to which of the following ions?
a) Sodium
b) Hydrogen
c) Nitrogen
d) Chlorine

View Answer

Answer: a [Reason:] In glass membrane electrode, the glass containing 11% Na2O, 18% Al2O3, 71% SiO2 is highly sensitive to sodium ions. Glass electrodes can be used to measure various ions by changing the glass membrane composition.

3. In liquid membrane electrode, the liquid ion exchanger is held in a porous disc of _____________
a) Solid material
b) Semi-permeable membrane
c) Hydrophobic material
d) Water absorbing material

View Answer

Answer: c [Reason:] In liquid membrane electrode, the liquid ion exchanger is held in a porous disc of hydrophobic material. It is a water repelling material.

4. In recent liquid membrane electrodes, the porous liquid membrane is replaced with which of the following?
a) Polyvinyl chloride
b) Polyacryl chloride
c) Polyester membrane
d) Polyacryl amide

View Answer

Answer: a [Reason:] In recent liquid membrane electrodes, the porous liquid membrane is replaced with polyvinyl chloride membrane. The measured potential is a direct measure of concentration of specific ion.

5. Which of the following is used in potassium electrode in liquid membrane electrodes?
a) Ionomycin
b) Valinomycin
c) Nonactin
d) Gramicidin

View Answer

Answer: b [Reason:] Valinomycin is used in potassium electrode in liquid membrane electrodes. It is a doughnut shaped electron rich pocket.

6. In solid state membranes, the body of the electrodes are made of which of the following?
a) Polyvinyl chloride
b) Plastic
c) Polythene
d) Teflon

View Answer

Answer: d [Reason:] In solid state membranes, the body of the electrodes are made of Teflon. The membrane is held in position using epoxy resin.

7. Which of the following is not the characteristic of ion selective electrodes?
a) Simple to use
b) Inexpensive
c) Narrow concentration range
d) Operates in wide range of temperature

View Answer

Answer: c [Reason:] Ion selective electrodes have wide concentration range. It is highly selective to a particular ion.

8. Ion selective electrode are unaffected by colour or turbidity of the solution.
a) True
b) False

View Answer

Answer: a [Reason:] Ion selective electrode are unaffected by colour or turbidity of the solution. It operates in wide range of temperature.

9. Which of the following is not a problem of ion selective electrodes?
a) Interference with other ions
b) Output is influences by ionic strength
c) Drift in electrode potential during a sequence of measurements
d) Can measure only positive ions

View Answer

Answer: d [Reason:] Ion selective electrodes can measure both positive and negative ions. It is affected by interference from other ions.

10. Which of the following is the effective concentration measured at the electrode head?
a) Selectivity co-efficient
b) Ionic strength
c) Activity
d) Activity co-efficient

View Answer

Answer: c [Reason:] Activity is the effective concentration measured at the electrode head. Concentration is different from activity.

11. The value of activity co-efficient is always in which of the following ranges?
a) Zero
b) Less than zero
c) Less than 1
d) Greater than 1

View Answer

Answer: c [Reason:] The value of activity co-efficient is always less than 1. It is the ratio of activity divided by concentration.

12. Which of the following specifies the relation between ionic strength and activity co-efficient?
a) Directly proportional
b) Inversely proportional
c) Equal
d) No particular relation

View Answer

Answer: b [Reason:] Activity co-efficient and ionic strength are inversely proportional to each other. If the ionic strength increases, the value of activity decreases.

13. The difference between measured activity and actual concentration becomes higher at higher concentration. Is this statement true or false?
a) True
b) False

View Answer

Answer: a [Reason:] The difference between measured activity and actual concentration becomes higher at higher concentration. Similarly, it decreases at lower concentrations.

14. Given below is the diagram of liquid membrane electrode. Identify the unmarked component.
a) Solid material
b) Semi-permeable membrane
c) Hydrophobic material
d) Water absorbing material

View Answer

Answer: c [Reason:] The unmarked component is porous hydrophobic material. It holds the liquid ion exchanger.

15. Ion selective electrodes have ________ linear range and _________ detection limit than the pH electrode.
a) Lower, lower
b) Lower, higher
c) Higher, lower
d) Higher, higher

View Answer

Answer: b [Reason:] Ion selective electrodes have lower linear range and higher detection limit than the pH electrode. It works on effectively narrow pH.

Set 5

1. In Ammonia electrode, diffusion of dissolved ammonia occurs through the membrane until which of the following conditions occur?
a) Concentration becomes equal on both sides
b) Activity becomes equal on both sides
c) Partial pressure becomes equal on both sides
d) Differential pressure is low

View Answer

Answer: c [Reason:] In Ammonia electrode, diffusion of dissolved ammonia occurs through the membrane until partial pressure becomes equal on both sides. Partial pressure is proportional to its concentration.

2. When electrode potential response is plotted as a function of ammonia concentration on a semi-log graph, the graph obtained will be ____________
a) A straight line
b) Parabolic
c) Sigmoidal
d) A curve

View Answer

Answer: a [Reason:] When electrode potential response is plotted as a function of ammonia concentration, the graph obtained will be a straight line. The slope will be about 58mV per decade.

3. How can samples above 1M in ammonia concentration be measured using ammonia electrode?
a) It must be diluted and measured
b) It cannot be measured
c) The electrode has to be modified for measuring
d) It can be measured directly

View Answer

Answer: a [Reason:] Samples above 1M in ammonia concentration be measured by diluting the solution. Samples having concentrations below that can be measured directly.

4. The dilution of solution must not reduce the level of ammonia below _________
a) 10-2 M
a) 10-5 M
a) 10-8 M
a) 10-9 M

View Answer

Answer: a [Reason:] The dilution of solution must not reduce the level of ammonia below 10-5 M. The total level of dissolved species must be below 1M.

5. Which of the following factors does not the reproducibility of the ammonia electrode?
a) Temperature
b) Drift
c) Noise
d) Dilution

View Answer

Answer: d [Reason:] Dilution does not affect reproducibility. The other three factors affect the reproducibility.

6. The performance of ammonia electrode is not affected by sample colour and turbidity.
a) True
b) False

View Answer

Answer: a [Reason:] The performance of ammonia electrode is not affected by sample colour and turbidity. Temperature affects its output.

7. In fluoride ion electrode, the potential corresponding to level of the fluoride ion is described by which of the following equations when E is the measured electrode potential, Eo is the reference potential and A is the level of fluoride ions in solution?
a) E=Eo+0.0591 log A
b) E=Eo-0.0591 log A
c) E=Eo+0.0896 log A
d) E=Eo-0.0896 log A

View Answer

Answer: b [Reason:] In fluoride ion electrode, the potential corresponding to level of the fluoride ion is described by the equation, E=Eo-0.0591 log A. A is the activity or effective concentration of fluoride ions.

8. What does TISAB which is used to overcome interferences stand for?
a) Total Isolation Strength Absolute Buffer
b) Total Ionic Strength Absolute Buffer
c) Total Ionic Strength Adjustment Buffer
d) Total Isolation Strength Adjustment Buffer

View Answer

Answer: c [Reason:] TISAB stands for ‘Total Ionic Strength Adjustment Buffer’. It is added in excessand in exactly the same amount to each of the solution that is to be measured.

9. Which of the following causes main interference in Fluoride electrode?
a) H+ ions
b) OH ions
c) Li+ ions
d) Cl ions

View Answer

Answer: b [Reason:] The main interference in fluoride ions is caused by OH ions. It has excellent selectivity.

10. Crystal membrane of ion selective electrode can be regenerated by washing with which of the following?
a) Alcohol
b) Iodine solution
c) Acidic solution
d) Basic solution

View Answer

Answer: a [Reason:] Crystal membrane of ion selective electrode can be regenerated by washing with alcohol. It can be gently polished with emery paper to remove deposits.

11. For fluoride electrode, the electrode response curve will not only shift but will change slope with changes in temperature.
a) True
b) False

View Answer

Answer: a [Reason:] For fluoride electrode, the electrode response curve will not only shift but will change slope with changes in temperature. A 1o change in temperature causes a 2% error.

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