MCQOPTIONS
Saved Bookmarks
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.
| 151. |
An electron in a metal suffers collision and if the probability of it being scattered over an angle dθ is 2π P(θ) sin θ dθ where P(θ) is an arbitrary function of scattering angle θ, then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 152. |
If v is velocity of electron, ε0 is absolute permittivity, m is mass of electron, e is charge on electron and r is the radius of orbit of electron in hydrogen atom, the stability of orbit requires the following equation to be satisfied |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 153. |
If a metal specimen has n valence electrons per m³ each having charge e and mass m and t is the relaxations time, the conductivity is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 154. |
As per Matthiessen's rule, the total resistivity r of a conductor can be written as ρ = ρi + aT, where ρi and a are constants and T is absolute temperature. At very low temperatures |
| A. | aT = 0 |
| B. | aT > ρi |
| C. | aT ∼ ρi |
| D. | aT < ρi |
| Answer» E. | |
| 155. |
A specimen of metal has n valence electrons per m³. If vx is the average velocity of these electrons, each having a charge e, the current density J is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 156. |
A metal has a large number of free electrons. If e is electronic charge and m is mass of electron and an electric field E is applied along (say) x direction, the electrons acquire a velocity having a component vx is x direction. Then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 157. |
A parallel plate capacitor has area of plate equal to 1 m and distance between plates is also 1 m². The lossy dielectric has a complex dielectric constant ∈r = ∈'r - j ∈"r. If the capacitor is represented by R and C is parallel, then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 158. |
The v-i characteristic shown in the given figure is for |
| A. | thermistor |
| B. | photoconductor |
| C. | varistor |
| D. | none of the above |
| Answer» D. none of the above | |
| 159. |
Two coaxial metallic cylinders have radii R1 and R2. The space between them is filled with a dielectric having dielectric constant ∈r. The capacitance per metre length is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 160. |
If m is the mass of electron cloud, the equation of motion of electron cloud in the presence of an alternating electric field is of the form |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 161. |
In p type semiconductor, the conductivity due to holes is (e = charge on hole, μp = hole mobility, p = hole concentration) |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 162. |
A vacuum parallel plate capacitor is charged. The field between the plates is 2 x 10⁴ V/m. If the space between the plates is filled with a material having ∈ᵣ = 10, then the value of field in the dielectric will be |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 163. |
Assertion (A): In Figure, the intercept of the line on y-axis is equal to N (ae + ai), where N is number of atoms/m³, ae is electronic polarizability and ai is ionic polarizability.Reason (R): ae and ai are independent of temperature. |
| 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 | |
| 164. |
Assertion (A): At a temperature of 1000 K, thermionic emission current is about 0.1 A/cm² of surface.Reason (R): Thermionic emission current is given by Ith = SA₀ T² e^(-Ew/kT). |
| 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 | |
| 165. |
If μp is permanent dipole moment and T is absolute temperature, the orientation polarization of polyatomic gases is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 166. |
For a polyatomic gas, the equation relating dielectric constant ∈ᵣ with molecular properties is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 167. |
If m, v, r are the mass, velocity and radius of orbit of electron and h is Planck's constant, quantum condition for electron's orbit is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 168. |
From a homogeneous and isotropic dielectric material of dielectric constant ∈r, 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. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 169. |
An electron is moving in a circular orbit of radius R at angular velocity ω₀ in a field free space. If a magnetic field B is created, the velocity of electron ω will be given by the equation |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 170. |
A material has N spins per m³. If Np are the dipoles per m³ parallel to field and Na are the dipoles per m³ anti-parallel to field, the magnetisation is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 171. |
A particle of charge Q coulombs is bound elastically to an equilibrium position with a force constant of f newton per metre. The polarizability of the system is |
| A. | Q/f |
| B. | Q²/f |
| C. | Q/f² |
| D. | Qf |
| Answer» C. Q/f² | |
| 172. |
∈ᵣ is determined by the atomic structure of the dielectric. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 173. |
As regards ferromagnetic Curie temperature Qf and paramagnetic curie temperature θ |
| A. | Qf > θ |
| B. | θ > Qf |
| C. | θ equal to or less than Qf |
| D. | θ may be equal to less than or more Qf |
| Answer» C. θ equal to or less than Qf | |
| 174. |
Assertion (A): If an electron having charge e is revolving in an orbit of radius R and with angular velocity ω, the magnetic dipole moment of orbit is 0.5 eωR².Reason (R): Orbital angular momentum and magnetic dipole moment are always equal. |
| 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» D. A is false but R is true | |
| 175. |
The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m²) and dT/dx (°C per metre) is |
| A. | Q = K(dT/dx) |
| B. | Q = - K(dT/dx) |
| C. | K = Q(dT/dx) |
| D. | dT/dx = - QK |
| Answer» C. K = Q(dT/dx) | |
| 176. |
If τ is relaxation time and τc is average time between collisions, then in an isotropic metal |
| A. | τ = τc |
| B. | τ < τc |
| C. | τc < τ |
| D. | T = 0.01 τe |
| Answer» B. τ < τc | |
| 177. |
For a diamagnetic material, μᵣ = 1. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 178. |
The dielectric constant of ferroelectric materials can be expressed by the equation |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 179. |
If the operating temperature increases by 10°C, the rate of deterioration of solid dielectric becomes |
| A. | double |
| B. | one and a half time |
| C. | 3 times |
| D. | 4 times |
| Answer» B. one and a half time | |
| 180. |
The electric dipole moment of a neutral system of point charges Q1, Q2.... is ∑Qiri . The charges Qi |
| A. | must be all positive |
| B. | must be all negative |
| C. | must be such that ∑Qi = 0 |
| D. | either (a) or (b) |
| Answer» D. either (a) or (b) | |
| 181. |
Assertion (A): If E is available energy state eV and EF is Fermi level, then probability of energy state E being occupied = 0.5.Reason (R): . |
| 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 | |
| 182. |
The orientation polarization is1. directly proportional to temperature2. inversely proportional to temperature3. inversely proportional to square of permanent dipole moment4. directly proportional to square of permanent dipole moment. Which of the above are correct? |
| A. | 1 and 3 only |
| B. | 2 and 3 only |
| C. | 1 and 4 only |
| D. | 2 and 4 only |
| Answer» E. | |
| 183. |
Which of the following are donor impurities?1. Gold2. Phosphorus3. Boron4. Antimony5. Arsenic6. Induim Select the correct answer using the following codes |
| A. | 1, 2, 3 |
| B. | 1, 2, 4, 6 |
| C. | 3, 4, 5, 6 |
| D. | 2, 4, 5 |
| Answer» E. | |
| 184. |
If e is the charge of an electron, R is the radius of its orbit and ω is the angular velocity of electron, the magnetic dipole moment μm of the orbit is |μm| = eωR². |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 185. |
The apparent capacitance at a high angular frequency ω of an air cored capacitor having capacitance C and inductance L is given by |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 186. |
Consider the following statements: |
| 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 | |
| 187. |
Consider the following statements : |
| 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 | |
| 188. |
If ∈r' and ∈r" are the real and imaginary parts of complex dielectric constant ∈r, and δ is the loss angle. Then |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 189. |
Assertion (A): From the slope of the line in Figure, we can find permanent dipole moment of the molecules.Reason (R): Total polarization of a polyatomic gas is given by P = N(ae + ai + μ²p / 3kT)E. |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 190. |
When a dielectric material is subjected to alternating field, the absorption of energy by the material from the field is given by the imaginary part of polarizability. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 191. |
Ferrimagnetic materials have anti parallel orientation of equal moments of permanent dipoles. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 192. |
Which of the following are true for relative dielectric constant?1. It is dimensionless.2. It is equal to 1 for vacuum.3. 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 | |
| 193. |
Schrodinger wave equation is a |
| A. | Linear equation |
| B. | Differential equation |
| C. | Partial differential equation |
| D. | None of the above |
| Answer» D. None of the above | |
| 194. |
Many compounds also exhibit semiconducting properties. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 195. |
An electron (charge -e) is rotating in a circular orbit of radius R, around a proton with charge +e at a constant angular velocity ω. The orbital magnetic dipole moment is |
| A. | 2 eω R2 |
| B. | 0.5 eω R3 |
| Answer» B. 0.5 eœâ R3 | |
| 196. |
Assertion (A): ‚ààr can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.Reason (R): Capacitance of a parallel plate capacitor = . |
| A. | A is true but R is false |
| B. | A is false but R is true |
| Answer» B. A is false but R is true | |
| 197. |
Ferrimagnetic materials have anti-parallel orientation of equal moments of permanent dipoles. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 198. |
Assertion (A): When an electron is revolving in its orbit and magnetic field is also present, the angular frequency of electron will be affected by the magnetic field.Reason (R): In the case of electron revolving in its orbit in the presence of magnetic field, the orbital magnetic dipole moment is not affected by the presence of magnetic field. |
| 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» D. A is false but R is true | |
| 199. |
Spontaneous magnetisation is characteristic of ferromagnetic materials. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 200. |
When a potential is applied across an intrinsic semiconductor, holes flow |
| A. | in the external circuit only |
| B. | none of the above |
| Answer» C. | |