MCQOPTIONS
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MCQOPTIONS
This section includes 595 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.
| 251. |
At a temperature of about 1 K, aluminium is a |
| A. | conductor |
| B. | insulator |
| C. | photoconductor |
| D. | superconductor |
| Answer» E. | |
| 252. |
At T = 0, the resistivity of a perfect single crystal of a metal is |
| A. | high |
| B. | finite |
| C. | electronic and orientational |
| D. | electronic and ionic |
| Answer» B. finite | |
| 253. |
Magnetic hysteresis phenomenon is explained by |
| A. | motion of domain walls |
| B. | motion of domain walls and domain rotation |
| C. | domain rotation |
| D. | none of the above |
| Answer» C. domain rotation | |
| 254. |
A photoconductor is a |
| A. | conductor |
| B. | semiconductor |
| C. | insulator |
| D. | superconductor |
| Answer» C. insulator | |
| 255. |
If temperature is increased, the temperature coefficient of a metal |
| A. | increases |
| B. | decreases |
| C. | may increase or decrease |
| D. | remains constant |
| Answer» C. may increase or decrease | |
| 256. |
The circumference of an electron orbit is equal to integer times the wavelength of electron. |
| A. | 1 |
| B. | |
| C. | 0.5 T |
| D. | less than 0.5 T |
| Answer» B. | |
| 257. |
The law that (where K is thermal conductivity, σ is electrical conductivity and T is absolute temperature) for all metals is equal to a universal constant is known as |
| A. | Curie Weiss law |
| B. | Kittel law |
| C. | 1 |
| D. | |
| Answer» B. Kittel law | |
| 258. |
A rare gas having N atoms/m3 is subjected to an electric field E. The electric dipole moment per unit volume is proportional to N and E. |
| A. | 1 |
| B. | |
| C. | the number of electrons-hole pairs generated per second due to thermal motion are equal to the number of electron-hole pairs lost per second due to recombination |
| D. | the number of electron-hole pairs generated per second due to thermal motion is always less than the number of electron-hole pairs lost per second due to recombination |
| Answer» B. | |
| 259. |
When a material is in superconducting state and a magnetic field is applied |
| A. | the superconducting property may be destroyed |
| B. | the material may become an insulator |
| C. | 1 |
| D. | |
| Answer» D. | |
| 260. |
Sulphur hexafluoride is used in |
| A. | relays |
| B. | circuit breakers |
| C. | 5 |
| D. | 4 |
| Answer» E. | |
| 261. |
Assertion (A): Magnetism can be explained by the theory of magnetic domains.Reason (R): The existence of magnetic domains is evident from the Bitter powder patterns. |
| A. | Both A and R are true and R is correct explanation of A |
| B. | Both A and R are true but R is not correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» C. A is true but R is false | |
| 262. |
In van der walls crystals, there exists a high degree of stability of the outer electron shell. |
| A. | 1 |
| B. | |
| C. | 7 |
| D. | 6 |
| Answer» B. | |
| 263. |
Specific resistance of silver is about |
| A. | 0.16 x 10-8 Ω-m |
| B. | 1.64 x 10-8 Ω-m |
| C. | 16 x 10-8 Ω-m |
| D. | 164 x 10-8 Ω-m |
| Answer» C. 16 x 10-8 Œ©-m | |
| 264. |
The units for electric dipole moment are |
| A. | coulombs |
| B. | colomb-metre |
| C. | coulomb/metre |
| D. | coulomb/m2 |
| Answer» C. coulomb/metre | |
| 265. |
Assertion (A): In a parallel plate capacitor having area of plate 1 m2 and plate separation 1 m, the capacitance C and resistance R are given by C = ∈0∈'r and R = where ω is frequency, ∈r' and ∈r" are real and imaginary parts of dielectric constant.Reason (R): The imaginary part of electric constant is responsible for dielectric losses. |
| A. | A is true but R is false |
| B. | A is false but R is true |
| C. | Both A and R are true and R is correct explanation of A |
| D. | Both A and R are true but R is not correct explanation of A |
| Answer» B. A is false but R is true | |
| 266. |
An electron in a metal suffers collision and if the probability of it being scattered over an angle dθ is 2p P(θ) sin θ dθ where P(θ) is an arbitrary function of scattering angle θ, then |
| A. | 2pP(θ) sin θ dθ = 0 |
| B. | 2pP(θ) sin θ dθ = 2 |
| C. | 2pP(θ) sin θ dθ = -1 |
| D. | 2pP(θ) sin θ dθ = 1 |
| Answer» D. 2pP(Œ∏) sin Œ∏ dŒ∏ = 1 | |
| 267. |
Paramagnetic materials have permanent magnetic dipoles but interaction between neighbouring dipoles is negligible. |
| A. | Both A and R are true and R is correct explanation of A |
| B. | Both A and R are true but R is not correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» B. Both A and R are true but R is not correct explanation of A | |
| 268. |
In a metal, the valence electrons |
| A. | are shared by all atoms |
| B. | either (b) or (c) |
| C. | 1 |
| D. | |
| Answer» D. | |
| 269. |
In which of the following semiconductor are holes minority carriers |
| A. | extrinsic |
| B. | p type |
| C. | n type |
| D. | intrinsic |
| Answer» D. intrinsic | |
| 270. |
Silicon and germanium have diamond structure. The number of atoms in a volume equal to a3 where a is the edge of elementary cube are |
| A. | 32 |
| B. | 16 |
| C. | 8 |
| D. | 4 |
| Answer» D. 4 | |
| 271. |
A sample of N type semiconductor has an electron density of 6.25 x 1018/cm3 at 300 K. If intrinsic concentration of carriers in this sample is 2.5 x 1013/cm3 at this temperature, the hole density is |
| A. | 1010 / cm3 |
| B. | 1012 / cm3 |
| C. | Both A and R are true and R is correct explanation of A |
| D. | Both A and R are true but R is not correct explanation of A |
| Answer» C. Both A and R are true and R is correct explanation of A | |
| 272. |
Electric dipole moment is usually expressed in debye units. Here, 1 debye unit equals |
| A. | 3.33 x 10-30 C-m |
| B. | 3.33 x 10-30 C-m2 |
| C. | 3.30 x 10-10 C-m |
| D. | 3.33 x 10-10 C-m2 |
| Answer» B. 3.33 x 10-30 C-m2 | |
| 273. |
Silicon and germanium atoms combine orderly into array of atoms located in repetitive geometric pattern. This pattern is called |
| A. | crystal |
| B. | covalent bond |
| C. | molecule |
| D. | valence bond |
| Answer» B. covalent bond | |
| 274. |
A copper specimen has resistivity equal to 1.8 x 10-8 ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be |
| A. | 1.6 x 10-8 Ω-m |
| B. | 2 x 10-8 Ω-m |
| C. | 3 x 10-8 Ω-m |
| D. | 6 x 10-8 Ω-m |
| Answer» E. | |
| 275. |
In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as |
| A. | Lattice constant |
| B. | Lorentz number |
| C. | Lanevin function |
| D. | Larmor number |
| Answer» C. Lanevin function | |
| 276. |
Transformer oil is |
| A. | refined vegetable oil |
| B. | refined mineral oil |
| C. | mixture of vegetable and mineral oil |
| D. | none of the above |
| Answer» C. mixture of vegetable and mineral oil | |
| 277. |
A liquid has N permanent dipoles μp per unit volume and has been subjected to dc field for a long time such that orientation polarization is P0. At t = 0, the field is suddenly removed, then polarization |
| A. | will remain constant at P0 |
| B. | will become zero at t = 0 |
| C. | will delay to zero with a time constant |
| D. | either b or c |
| Answer» D. either b or c | |
| 278. |
The rule that resistivity of conductors can be separated into two parts viz. temperature independent and temperature dependent is known as |
| A. | Matthiessen's rule |
| B. | Debye rule |
| C. | Curie rule |
| D. | Onne's rule |
| Answer» B. Debye rule | |
| 279. |
When a trivalent impurity is added, the semiconductor becomes |
| A. | p type |
| B. | n type |
| C. | intrinsic |
| D. | neutral |
| Answer» B. n type | |
| 280. |
When a ferromagnetic substance is magnetised there are small changes in dimensions. This phenomenon is called |
| A. | diamagnetism |
| B. | dipolar relaxation |
| C. | Both A and R are true and R is correct explanation of A |
| D. | Both A and R are true but R is not correct explanation of A |
| Answer» C. Both A and R are true and R is correct explanation of A | |
| 281. |
Assertion (A): Dielectric losses are proportional to tan δ.Reason (R): tan δ = where ∈r' and ∈r" denote the real and imaginary parts of ∈r. |
| A. | A is true but R is false |
| B. | A is false but R is true |
| C. | 0 |
| D. | low |
| Answer» B. A is false but R is true | |
| 282. |
When an atom of polarizability a is placed in an electric field E, the energy stored in atom is 0.5 a E2. |
| A. | 1.6 x 10-19 C |
| B. | 2.6 x 10-19 C |
| C. | 0.6 x 10-19 C |
| D. | 1.6 x 10-13 C |
| Answer» B. 2.6 x 10-19 C | |
| 283. |
A good dielectric should have |
| A. | low losses |
| B. | good heat conductivity |
| C. | high intrinsic strength |
| D. | all of the above |
| Answer» E. | |
| 284. |
The amount of time between the creation and recombination of a free electron and hole is called |
| A. | relaxation time |
| B. | life time |
| C. | lorentz time |
| D. | collision time |
| Answer» C. lorentz time | |
| 285. |
A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be |
| A. | 2.5 mH |
| B. | 5 mH |
| C. | 20 mH |
| D. | 40 mH |
| Answer» E. | |
| 286. |
An atom of polarizability a is placed in a homogeneous electric field E. The energy stored in polarized atom is |
| A. | aE2 |
| B. | aE |
| C. | 1 |
| D. | |
| Answer» D. | |
| 287. |
A magnet does not attract |
| A. | nickel |
| B. | iron |
| C. | copper |
| D. | iron and copper |
| Answer» D. iron and copper | |
| 288. |
The capacitance of an insulated conducting sphere of radius R in vacuum is |
| A. | 2p‚àà0R |
| B. | 4p‚àà0R |
| C. | 4p‚àà0R2 |
| D. | 4p |
| Answer» C. 4p‚àà0R2 | |
| 289. |
The mass of proton and electron are |
| A. | 1.672 x 10-26 kg and 9.107 x 10-31 kg respectively |
| B. | 9.107 x 10-26 kg and 9.107 x 10-31 kg respectively |
| C. | 9.107 x 10-29 kg and 9.107 x 10-31 kg respectively |
| D. | 9.107 x 10-30 kg and 9.107 x 10-31 kg respectively |
| Answer» B. 9.107 x 10-26 kg and 9.107 x 10-31 kg respectively | |
| 290. |
If Bmax is the maximum flux density, hysteresis loss is proportional to |
| A. | B2max |
| B. | B3max |
| C. | high permittivity |
| D. | low permittivity |
| Answer» C. high permittivity | |
| 291. |
Which of the following are true for relative dielectric constant? It is dimensionless.It is equal to 1 for vacuum.It is equal to 1 for all substances. |
| A. | 1 and 2 only |
| B. | 2 and 3 only |
| C. | 1 and 3 only |
| D. | 1, 2 and 3 |
| Answer» B. 2 and 3 only | |
| 292. |
Electric dipole moment is expressed in debye unit. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 293. |
The number of protons in a copper atom are |
| A. | 11 |
| B. | 29 |
| C. | the superconducting property is not affected |
| D. | the superconducting property may be affected and resistivity may increase from zero to a low value |
| Answer» E. | |
| 294. |
The number of protons in germanium atom is |
| A. | 28 |
| B. | 32 |
| C. | transformers |
| D. | generators |
| Answer» E. | |
| 295. |
Assertion (A): The equation D = ‚àà0‚ààrE is applicable only to isotropic materials.Reason (R): In polycrystalline materials, the directional effects are absent. |
| A. | Both A and R are true and R is correct explanation of A |
| B. | Both A and R are true but R is not correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» C. A is true but R is false | |
| 296. |
From a homogeneous and isotropic dielectric material of dielectric constant ‚ààr, a small volume element is taken out creating a cavity. The field can be kept homogeneous if Di. (i.e., electric flux density inside the cavity) and D0 (i.e., electric flux density outside the cavity) are such that |
| A. | |
| B. | either (a) or (b) |
| C. | ac only |
| Answer» C. ac only | |
| 297. |
An electron for which l = 0 has zero orbital magnetic dipole moment. |
| A. | 1 |
| B. | |
| C. | increase as f increase |
| D. | decrease as f increase |
| Answer» B. | |
| 298. |
The units for intrinsic strength of dielectric are |
| A. | kV |
| B. | kV/m |
| C. | A |
| D. | A/m |
| Answer» C. A | |
| 299. |
Assertion (A): Rochelle salt and Barium titanate are both ferroelectric. Reason (R): Ferroelectric materials exhibit hysteresis effect. |
| A. | Both A and R are true and R is correct explanation of A |
| B. | Both A and R are true but R is not correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» C. A is true but R is false | |
| 300. |
A magnetic field exists around |
| A. | moving charges |
| B. | static charges |
| C. | iron |
| D. | copper |
| Answer» B. static charges | |