MCQOPTIONS
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MCQOPTIONS
This section includes 1085 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 651. |
Ionospheric storm causes an abnormal decrease in the critical frequency. |
| A. | 1 |
| B. | |
| C. | Discone |
| D. | Helical |
| Answer» B. | |
| 652. |
The virtual height of an ionospheric layer is __________ true height |
| A. | equal to |
| B. | less than |
| C. | higher than |
| D. | no relation |
| Answer» D. no relation | |
| 653. |
Alternating current can induce voltage because it has magnetic field which is |
| A. | constant |
| B. | time varying |
| C. | stronger field than D.C. |
| D. | closed loop nature. |
| Answer» C. stronger field than D.C. | |
| 654. |
When a plane wave is incident normally from dielectric '1' (μ0, ε1) onto dielectric '2' (μ0, ε2) the electric field of the transmitted wave is 2 times the electric field of the reflected wave. The ratio ε2/ε1 is |
| A. | 0.5 |
| B. | 1 |
| C. | 2 |
| D. | 4 |
| Answer» E. | |
| 655. |
The static electric field in a conductor is |
| A. | zero |
| B. | unity |
| C. | infinity |
| D. | none of the above |
| Answer» B. unity | |
| 656. |
In waveguides the existing waves are |
| A. | both (a) and (b) |
| B. | all of the above |
| C. | fading |
| D. | Faraday rotation |
| Answer» E. | |
| 657. |
For a reflection co-efficient of 0.5, the value of SWR is |
| A. | -1 |
| B. | 1 |
| C. | 2 |
| D. | 3 |
| Answer» E. | |
| 658. |
The gain of an half wavelength antenna is |
| A. | 2.15 dB |
| B. | 10 dB |
| C. | 1.78 dB |
| D. | 100 dB |
| Answer» B. 10 dB | |
| 659. |
The impedance inversion may be objected with |
| A. | a short-circuited stub |
| B. | an open-circuited stub |
| C. | a half-wave line |
| D. | a quarter-wave line |
| Answer» E. | |
| 660. |
Long distance short wave radio broadcasting based on |
| A. | line of sight |
| B. | ionospheric wave |
| C. | ground wave |
| D. | skywave |
| Answer» C. ground wave | |
| 661. |
VLF is generally used for |
| A. | telegraphy |
| B. | satellite communication |
| C. | instrument landing system |
| D. | all of the above |
| Answer» B. satellite communication | |
| 662. |
Which of the following is not an omnidirectional antenna? |
| A. | Log periodic |
| B. | Half-wave dipole |
| C. | Discone |
| D. | Marconi |
| Answer» B. Half-wave dipole | |
| 663. |
Radar antennas are |
| A. | dipoles |
| B. | helical |
| C. | parabolic |
| D. | conical |
| Answer» D. conical | |
| 664. |
Antenna used for direction finding is |
| A. | long dipole |
| B. | parabolic |
| C. | rhombic |
| D. | helical |
| Answer» B. parabolic | |
| 665. |
Microwave signals follow the curvature of the earth and the phenomenon |
| A. | tropospheric scatter |
| B. | faraday effect |
| C. | duct propagation |
| D. | none |
| Answer» D. none | |
| 666. |
The numerical value of directivity of current element of half-wave dipole is 1.76 and 2.15 dB respectively. The directive gain of half-wave dipole over current element will be |
| A. | 3.91 dB |
| B. | 1.95 dB |
| C. | 0.39 dB |
| D. | 0.195 dB |
| Answer» D. 0.195 dB | |
| 667. |
In a turnstile antenna the crossed dipoles are excited with voltages |
| A. | in phase with each other |
| B. | 90° out of phase with each other |
| C. | 120° out of phase with each other |
| D. | 180° out of phase with each other |
| Answer» C. 120¬∞ out of phase with each other | |
| 668. |
The disturbance from adjacent power lines is known as |
| A. | cross talk |
| B. | cross fire |
| C. | inductive disturbance |
| D. | none of the above |
| Answer» D. none of the above | |
| 669. |
Short-circuited stubs are used, because open-circuited stubs are |
| A. | liable to radiate |
| B. | complex in nature |
| C. | providing open-circuit environments |
| D. | unable to provide work over large frequency range |
| Answer» B. complex in nature | |
| 670. |
Voltage standing wave pattern in a loss less transmission line with characteristic impedance 50 Ω and a resistive load is shown in the figure. The value of load resistance is |
| A. | 50 Ω |
| B. | 200 Ω |
| C. | 12.5 Ω |
| D. | 0 Ω |
| Answer» C. 12.5 Œ© | |
| 671. |
Which of the following relations is valid for a spherical surface? |
| A. | |
| B. | None of the above |
| C. | skin effect |
| Answer» D. | |
| 672. |
Tropospheric scatter propagation is not subject to any fading. |
| A. | 1 |
| B. | |
| C. | very high |
| D. | very low |
| Answer» C. very high | |
| 673. |
Diffraction of electromagnetic wave |
| A. | is caused by reflection from the ground |
| B. | may occur around the edge of a sharp obstacle |
| C. | arises only with spherical wavefronts |
| D. | none of these |
| Answer» C. arises only with spherical wavefronts | |
| 674. |
When a particular mode is excited in a waveguide, these appears an extra electric components in the direction of propagation. The resulting mode is |
| A. | Transverse electric |
| B. | Transverse magnetic |
| C. | Longitudinal |
| D. | Transverse Electromagnetic |
| Answer» C. Longitudinal | |
| 675. |
Electromagnetic cavity resonators (energy storage devices) are used in |
| A. | wave meters |
| B. | bandpass filters |
| C. | high frequency tubes |
| D. | all of the above |
| Answer» E. | |
| 676. |
The phase velocity in a coaxial line is |
| A. | greater than C |
| B. | equal to C |
| C. | less than C |
| D. | not depend on C |
| Answer» B. equal to C | |
| 677. |
Characteristic wave impedance is |
| A. | ε/μ |
| B. | (ε/μ)1/2 |
| C. | Ex/Hy |
| D. | Hy/Ex |
| Answer» C. Ex/Hy | |
| 678. |
The value of susceptibility in case of vacuum is taken as |
| A. | zero |
| B. | 0.5 |
| C. | unity |
| D. | infinity |
| Answer» B. 0.5 | |
| 679. |
If a EM wave propagating in z direction then |
| A. | component of EM wave will exist in z direction |
| B. | component of EM wave will not exist in z direction |
| C. | component of EM wave will exist in y direction |
| D. | component of EM wave will exist in x direction |
| Answer» C. component of EM wave will exist in y direction | |
| 680. |
Voltage standing wave pattern in a loss less transmission line with characteristic impedance 50 Ω and a resistive load is shown in the figure. Reflection coefficient is given by |
| A. | -0.6 |
| B. | -1 |
| C. | 0.6 |
| D. | 0 |
| Answer» D. 0 | |
| 681. |
A transmission line has characteristics impedance of (75 + j 0.01) Ω and is terminated in a load impedance of (70 + j 50) Ω. The transmission coefficient will be |
| A. | 1.70 - j 2.97 |
| B. | 0.08 + j 0.32 |
| C. | 1.32 + j 1.38 |
| D. | 1.08 + j 0.32 |
| Answer» E. | |
| 682. |
For a 400 kHz transmission line having L = 0.5 mH/km, C = 0.08 mF and negligible R and G, the velocity propagation will be |
| A. | 15.8303 km/s |
| B. | 15.830 km/s |
| C. | 1.583 km/s |
| D. | 0.1583 km/s |
| Answer» B. 15.830 km/s | |
| 683. |
The gain of an antenna with a circular aperture of diameter 3 metres at a frequency of 5 GHz, will be |
| A. | 2.4674 |
| B. | 24.674 |
| C. | 246.74 |
| D. | 24674 |
| Answer» E. | |
| 684. |
Reflectors and lens antennas are commonly used |
| A. | in LF communication systems |
| B. | not beyond 100 kHz |
| C. | in the range 10 MHz to 100 MHz |
| D. | above 100 MHz |
| Answer» E. | |
| 685. |
For a good conducting medium the intrinsic impedance is |
| A. | σωμ ∠p/2 |
| B. | ωμ /σ ∠45° |
| C. | ωμ/σ ∠p/2 |
| D. | ωμ/σ ∠0° |
| Answer» C. œâŒº/œÉ ‚à†p/2 | |
| 686. |
Directivity of antenna is defined as |
| A. | maximum directive gain |
| B. | average directive gain |
| C. | ‚àû |
| D. | 0 |
| Answer» B. average directive gain | |
| 687. |
Polarization of a wave is |
| A. | direction of electric field |
| B. | direction of magnetic field at some fixed point in space |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» B. direction of magnetic field at some fixed point in space | |
| 688. |
The ground waves eventually disappear as one moves away from the transmitter because of |
| A. | tilting |
| B. | maximum single-hop distance limitation |
| C. | interference from the sky waves |
| D. | loss of line-of sight condition |
| Answer» B. maximum single-hop distance limitation | |
| 689. |
A loop antenna may be of |
| A. | square on triangular shape |
| B. | hexagonal shape |
| C. | circular shape |
| D. | any of the above |
| Answer» E. | |
| 690. |
The transmitting antennas for lower frequencies (below 500 kHz) are generally |
| A. | vertical grounded wire type |
| B. | horizontal suspended wire type |
| C. | parabolic reflector type |
| D. | any of the above |
| Answer» B. horizontal suspended wire type | |
| 691. |
The skip distance is the maximum distance upto which ionospheric reflection is possible. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 692. |
When a current carrying conductor is brought into magnetic field, the force that moves the conductor depends upon |
| A. | the value of current |
| B. | the weight of the conductor |
| C. | the direction of the conductor |
| D. | none of the above |
| Answer» B. the weight of the conductor | |
| 693. |
The skip distance does not depends upon |
| A. | the power transmitted |
| B. | type of wave propagation |
| C. | angle of beaming of the wave |
| D. | frequency of the signal transmitted |
| Answer» C. angle of beaming of the wave | |
| 694. |
The total field produced by an antenna array system at a distance from it is |
| A. | sum of the field produced by the individual antennas of the array system |
| B. | directional gain of antenna |
| C. | linear antenna gain |
| D. | vector sum of the field produced by the individual antennas of the array system |
| Answer» E. | |
| 695. |
The thin parallel wires are carrying current along the same direction. The force experienced by one due to the other is |
| A. | parallel to the lines |
| B. | perpendicular to the lines and attractive |
| C. | perpendicular to the lines and repulsive |
| D. | zero |
| Answer» C. perpendicular to the lines and repulsive | |
| 696. |
An electromagnetic wave is incident normally on a dielectric boundary. It is |
| A. | totally reflected |
| B. | partially reflected and partially refracted |
| C. | totally absorbed |
| D. | none of the above |
| Answer» C. totally absorbed | |
| 697. |
Which of the following relations is valid? |
| A. | ‚àá x ‚àá x = ‚àá(‚àá . ) - ‚àá2 A |
| B. | ‚àá x ‚àá x = ‚àá(‚àá x ) - ‚àá2 A |
| C. | ‚àá x ‚àá x = ‚àá2 A - (‚àá) |
| D. | none of the above |
| Answer» B. ‚àá x ‚àá x = ‚àá(‚àá x ) - ‚àá2 A | |
| 698. |
In microwave communication, some times, microwave signals reach large distances by following the earth curvature. This phenomenon is called |
| A. | tropospheric scatter |
| B. | faraday effect |
| C. | ionospheric reflection |
| D. | ducting |
| Answer» E. | |
| 699. |
The ratio of tangential component of electric field at the surface of a conductor and the linear current density resulting from this field is __________ impedance |
| A. | characteristic |
| B. | critical |
| C. | surface |
| D. | polarizing |
| Answer» D. polarizing | |
| 700. |
Directivity gain depends on |
| A. | the distribution of radiated power in space |
| B. | solid angle of the radiated field pattern |
| C. | both (a) and (b) |
| D. | none of the above |
| Answer» B. solid angle of the radiated field pattern | |