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.
| 351. |
Characteristic impedance of a transmission line is 50 Ω. Input impedance of the open circuited line. Zoc = 100 + J150 Ω. When transmission line is short circuited, then value of the input impedance will be |
| A. | 50 Ω |
| B. | 100 + J150 Ω |
| C. | 7.69 + J11.54Ω |
| D. | 7.69 - J11.54 Ω |
| Answer» E. | |
| 352. |
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 Ω | |
| 353. |
If and the time average Poynting vector is |
| A. | null vector |
| B. | [B]. |
| C. | [C]. |
| D. | [D]. |
| Answer» B. [B]. | |
| 354. |
Consider a 300 Ω, quarter wave long at 1 GHz transmission line as shown in figure. It is connected to a 10 V, 50 Ω source at one end is left open circuited at the other end. The magnitude of the voltage at the open circuit end of the line is |
| A. | 10 V |
| B. | 5 V |
| C. | 60 V |
| D. | 60/7 volt |
| Answer» B. 5 V | |
| 355. |
Medium 1 has the electrical permittivity ε1 = 1.5 ε0 farad/m and occupies the region to the left of x = 0 plane. Medium 2 has the electrical permittivity ε2 = 2.5 ε0 farad/m and the occupies the region to the right of x = 0 plane. If E1 in medium 1 is volt/m, then E2 in medium 2 is |
| A. | [A]. |
| B. | [B]. |
| C. | [C]. |
| D. | [D]. |
| Answer» D. [D]. | |
| 356. |
The electric field on the surface of a perfect conductor is 2V/m. The conductor is immersed in water with ε = 80 ε0. The surface charge density on the conductor is ((ε0 = 10-9/36p)F/m) |
| A. | 0 c/m2 |
| B. | 2 c/m2 |
| C. | 1.8 x 10-11 c/m2 |
| D. | 1.14 x 10-9 c/m2 |
| Answer» E. | |
| 357. |
Distilled water at 25°C is characterized by σ = 1.7 x 10-4 mho/m and ε = 78 ε0 at a frequency of 3 GHz. Its loss tangent is (ε = 10-9/36p F/m) |
| A. | 1.3 x 10-5 |
| B. | 1.3 x 10-3 |
| C. | 1.7 x 10-4/78 |
| D. | 1.7 x l0-4/78ε0 |
| Answer» B. 1.3 x 10-3 | |
| 358. |
If a plane electromagnetic wave satisfies the equation , the wave propagates in the (at an angle of 45° between the x and z direction) |
| A. | x-direction |
| B. | z-direction |
| C. | y direction |
| D. | xy plane |
| Answer» C. y direction | |
| 359. |
A circular waveguide carries TE11 mode whose radial electric-field is given by Er = E 0J1 (r) sin φ V/m where 'r' is the radial distance in cm, from the waveguide axis. The cut-off wavelength of the mode is |
| A. | 10 cm |
| B. | 3p cm |
| C. | 2p cm |
| D. | 8 cm |
| Answer» D. 8 cm | |
| 360. |
Δ2V = - r/E is known as __________ equation |
| A. | Poisson |
| B. | Fourier |
| C. | Laplace |
| D. | Maxwell |
| Answer» B. Fourier | |
| 361. |
The attenuation factor a and phase shift factor β for a wave propagated in a good dielectric having are given by |
| A. | a = μ/ε , β = ωμ/ε |
| B. | a = β = μ/ε |
| C. | a = μ/ε , β = ωμ/ε |
| D. | a = β = ωμ/ε |
| Answer» B. a = β = μ/ε | |
| 362. |
∇ . = 0 is frequently known as |
| A. | continuity equation for steady currents |
| B. | Laplace equation |
| C. | Poisson's equation |
| D. | none of the above |
| Answer» B. Laplace equation | |
| 363. |
If a electromagnetic signal is incident at 0° in a waveguide then at other port of waveguide we will get |
| A. | zero power |
| B. | ∞ power |
| C. | depend upon input signal strength |
| D. | depend on frequency |
| Answer» B. ∞ power | |
| 364. |
A uniform plane wave travelling in air is incident on the plane boundary between air and another dielectric medium with εr = 4. The reflection coefficient for the normal incidence is |
| A. | zero |
| B. | 0.5 ∠180° |
| C. | 0.33 ∠0° |
| D. | 0.33 ∠180° |
| Answer» E. | |
| 365. |
A circular waveguide carries TE11 mode whose radial electric-field is given by Er = E₀J1 (r) sin φ V/m where 'r' is the radial distance in cm, from the waveguide axis. The cut-off wavelength of the mode is |
| A. | 10 cm |
| B. | 3π cm |
| C. | 2π cm |
| D. | 8 cm |
| Answer» D. 8 cm | |
| 366. |
If the electric field intensity associated with a uniform plane electromagnetic wave travelling in a perfect dielectric medium is given by E(z, t) = 10 cos (2π x 10⁷t - 0.1 πz) volt/metre, then the velocity of the travelling wave is |
| A. | 3.0 x 10⁸ m/sec |
| B. | 2 x 10⁸ m/sec |
| C. | 6.28 x 10⁷ m/sec |
| D. | 2 x 10⁷ m/sec |
| Answer» C. 6.28 x 10⁷ m/sec | |
| 367. |
The frequencies in ultra high frequency range are propagated by means of __________ waves |
| A. | surface |
| B. | ground |
| C. | sky |
| D. | space |
| Answer» E. | |
| 368. |
Q-factor of a transmission line at resonance is |
| A. | ωL/R |
| B. | L/R |
| C. | R/ωL |
| D. | L/CR |
| Answer» B. L/R | |
| 369. |
Characteristic impedance of a transmission line is 50 Ω. Input impedance of the open circuited line. Zoc = 100 + J150 Ω. When transmission line is short circuited, then value of the input impedance will be |
| A. | 50 Ω |
| B. | 100 + J150 Ω |
| C. | 7.69 + J11.54Ω |
| D. | 7.69 - J11.54 Ω |
| Answer» E. | |
| 370. |
The electric field on the surface of a perfect conductor is 2V/m. The conductor is immersed in water with ε = 80 ε0. The surface charge density on the conductor is ((ε0 = 10¯⁹/36π)F/m) |
| A. | 0 c/m² |
| B. | 2 c/m² |
| C. | 1.8 x 10¯¹¹ c/m² |
| D. | 1.14 x 10¯⁹ c/m² |
| Answer» E. | |
| 371. |
Consider the following; for a loss-less transmission line we can write, 1. Zin = - jz0 for a shorted line with l = λ/82. Zin = ± j ∞ for a shorted line with l = λ/43. Zin= jz0 for an open line with l = λ/24. Zin = 0 for a matched line of any length Select the correct answer using the codes given below codes. |
| A. | 1, 2 |
| B. | 2, 3 |
| C. | 1, 3 |
| D. | 2, 4 |
| Answer» E. | |
| 372. |
The Depth of penetration of EM wave in medium having conductivity σ at a frequency of 1 MHz is 25 cm. The depth of penetration at a frequency of 4 MHz will be |
| A. | 6.25 cm |
| B. | 12.50 cm |
| C. | 50 cm |
| D. | 100 cm |
| Answer» C. 50 cm | |
| 373. |
∇. J̅ = 0 is frequently known as |
| A. | continuity equation for steady currents |
| B. | Laplace equation |
| C. | Poisson's equation |
| D. | none of the above |
| Answer» B. Laplace equation | |
| 374. |
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. | |
| 375. |
A medium of relative permittivity εr2 = 2 forms an interface with free space. A point source of EM energy is located in the medium at a depth of 1 meter from the interface. Due to the total internal reflection, the transmitted beam has a circular cross-section over the interface. The area of the beam cross section at the interface is given by |
| A. | 2π m² |
| B. | π² m² |
| C. | π/2 m² |
| D. | π m² |
| Answer» E. | |
| 376. |
Find the noise factor for an antenna at 27°C with equivalent noise temperature 30°K |
| A. | 20 |
| B. | 100 |
| C. | 300 |
| D. | 1.1 |
| Answer» E. | |
| 377. |
Absolute permeability (μ) is given by __________ henry/metre |
| A. | 4π x 10¯¹² |
| B. | 4π x 10¯⁷ |
| C. | 8.854 x 10¯¹² |
| D. | 8.854 x 10¯⁷ |
| Answer» C. 8.854 x 10¯¹² | |
| 378. |
An open wire transmission line having a characteristic impedance of 600 ohms is terminated by a resistive load of 900 Ω. The standing wave ratio will be |
| A. | 1.5 |
| B. | 2.5 |
| C. | 3.5 |
| D. | 4.5 |
| Answer» B. 2.5 | |
| 379. |
The input impedance of short-circuited line of length l where l < λ/4 |
| A. | inductive |
| B. | capacitive |
| C. | resistive |
| D. | none of the above |
| Answer» B. capacitive | |
| 380. |
The number of free electrons in acceptor atom is |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» D. 4 | |
| 381. |
In a medium if ε, μ and σ are constant throughout the medium, then it is known as |
| A. | perfect vacuum |
| B. | distributed medium |
| C. | homogeneous medium |
| D. | dielectric medium |
| Answer» D. dielectric medium | |
| 382. |
A rectangular waveguide having TE₁₀ mode as dominant mode is having a cut off frequency of 18 GHz for the TE₃₀ mode. The inner broad wall dimension of the rectangular waveguide is |
| A. | 5/3 cm |
| B. | 5 cm |
| C. | 5/2 cm |
| D. | 10 cm |
| Answer» D. 10 cm | |
| 383. |
A vertical earthed antenna is resonant when its physical height is equal to |
| A. | λ |
| B. | λ/2 |
| C. | λ/4 |
| D. | λ/8 |
| Answer» D. λ/8 | |
| 384. |
The refractive index of E layer at frequency of √(81N) |
| A. | 0 |
| B. | ∞ |
| C. | 1 |
| D. | 0.5 |
| Answer» B. ∞ | |
| 385. |
Calculate the directivity of an antenna for θE = 30°, θH = 60 |
| A. | 46 |
| B. | 23 |
| C. | 50 |
| D. | 100 |
| Answer» C. 50 | |
| 386. |
A rectangular metal waveguide filled with a dielectric of relative permittivity εr = 4, has the inside dimensions 3 x 1.2 cm, the cut off frequency for the dominant mode is |
| A. | 2.5 GHz |
| B. | 5 GHz |
| C. | 10 GHz |
| D. | 12.5 GHz |
| Answer» C. 10 GHz | |
| 387. |
Polystyrene has a relative permittivity of 2.7. If the wave is incident at an angle θi of 30° from air into polystyrene, the angle of transmission will be nearly |
| A. | 0.2° |
| B. | 2° |
| C. | 18° |
| D. | 48° |
| Answer» D. 48° | |
| 388. |
The incidence from dielectric medium 1 (ε1) into dielectric medium 2 (ε2), Brewster angle θB and the corresponding angle of transmission θt for ε2/ε1 = 3 will be respectively |
| A. | 30° and 30° |
| B. | 30° and 60° |
| C. | 60° and 30° |
| D. | 30° and 60° |
| Answer» D. 30° and 60° | |
| 389. |
The directivity of 20 turn helix having α = 12° circumference equal to one wavelength, will be |
| A. | 1.8 dB |
| B. | 6 dB |
| C. | 12 dB |
| D. | 18 dB |
| Answer» E. | |
| 390. |
A 10 GHz signal propagates in a waveguide with a phase velocity of 4 x 10⁸ m/s. If the signal produces standing wave in the guide, then the distance between successive minimal will be |
| A. | 10 mm |
| B. | 20 mm |
| C. | 30 mm |
| D. | 40 mm |
| Answer» C. 30 mm | |
| 391. |
When the height of a vertical earthed antenna is less than λ/4 |
| A. | the base input impedance will be capacitive |
| B. | the base input impedance will be purely resistive |
| C. | the base input impedance will be inductive |
| D. | the base input impedance will be negligibly small |
| Answer» B. the base input impedance will be purely resistive | |
| 392. |
End fire array has a dipole spacing of λ/2. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 393. |
If wave of critical frequency 30 MHz is departing at an angle of 60°, then the MUF is given to be |
| A. | 10 MHz |
| B. | 15 MHz |
| C. | 30 MHz |
| D. | 60 MHz |
| Answer» E. | |
| 394. |
The cut off wavelength λc for TE₂₀ mode for a standard rectangles waveguide is |
| A. | 2/a |
| B. | 2a |
| C. | a |
| D. | 2a² |
| Answer» D. 2a² | |
| 395. |
For F1 layer the maximum ionic density is 2.3 x 10⁴ electrons per cc. The critical frequency for this layer will be |
| A. | 1.36 MHz |
| B. | 13.6 MHz |
| C. | 136 MHz |
| D. | 1360 MHz |
| Answer» C. 136 MHz | |
| 396. |
The maximum effective aperture of λ/2 (half-wave) antenna is |
| A. | 0.013 λ² |
| B. | 0.13 λ² |
| C. | 1.3 λ² |
| D. | 13 λ² |
| Answer» C. 1.3 λ² | |
| 397. |
Which of the following is a vector quantity? |
| A. | Standing wave ratio |
| B. | Reflection coefficient |
| C. | Gain |
| D. | All of the above |
| Answer» C. Gain | |
| 398. |
The radiation resistance of a λ/16 wire dipole in free space will be nearly |
| A. | 1 Ω |
| B. | 3 Ω |
| C. | 13 Ω |
| D. | 30 Ω |
| Answer» C. 13 Ω | |
| 399. |
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 reflection coefficient will be |
| A. | 0.08 + j 0.32 |
| B. | 0.32 + j 1.38 |
| C. | 0.70 - j 2.97 |
| D. | 1.1 + j 0.32 |
| Answer» B. 0.32 + j 1.38 | |
| 400. |
Magnetic susceptibility of a medium is the ratio of |
| A. | magnetic field strength to mmf |
| B. | intensity of magnetization to magnetic flux density |
| C. | intensity of magnetization to field strength |
| D. | mmf to magnetic field strength |
| Answer» D. mmf to magnetic field strength | |