Electromagnetic Theory MCQ

No, Wrong. This is calculated using:

λ=c/f= 3 x 10^8 / 6 x 10^9 = 0.05 m

Thus, higher frequency → shorter wavelength.

No, Wrong. The Coulomb law can be formulated from the Gauss law, using the divergence theorem. Thus it is an implication of Gauss law.

No, Wrong. The standard unit of charge is Coulomb. One coulomb is defined as the 1 Newton of force applied on 1 unit of electric field.

No, Wrong.
Superconducting materials depends only on the applied magnetic field, resultant magnetization at the temperature considered. It is independent of the applied electric field and the corresponding polarization.

No, Wrong.
Due to perfect diamagnetism in a superconductor, its magnetic susceptibility will be negative. This phenomenon is called Meissner effect.

No, Wrong.
Superconductors are characterised by diamagnetism behaviour and zero resistivity, which true for a dielectric. They occur only at low temperature. Thus a dielectric can become a superconductor at low temperatures with very high dielectric breakdown voltage.

No, Wrong.
On increasing the temperature, the free electrons in an insulator can be promoted from valence to conduction band. Gradually, it can act as a conductor through heating process. This condition is called dielectric breakdown, wherein the insulator loses its dielectric property and starts to conduct.

No, Wrong.
Iron and magnesium are metals. Hence they need not be considered. Both ceramics and plastic are insulators. But dielectric constant is more for ceramics always. Hence ceramics is the best dielectric.

No, Wrong.
The line integral of H is given by ∫H. dl. From Ampere law it can be related to the current density and hence the current element NI for a coil of N turns. Thus, ∫H. dl = NI.

No, Wrong.
The reluctance of a magnetic material is the ability of the material to oppose the magnetic flux. It is the ratio of the magnetic motive force mmf to the flux.

No, Wrong.
Flux lines are the magnetic lines of force of a magnetic material. Since the flux is overlapping, the total flux of the two coils together will be high. Thus it is an aiding flux. Also this type of overlapping is possible only when the two coils are back to back or in series connection.

No, Wrong.
The energy in a magnetic material is due to the formation of magnetic dipoles which are held together due to magnetic force. This gives energy to the material. Hence it is due to magnetization process.

No, Wrong.
The induced emf in a material under the influence of a magnetic field will oppose the flux that produces it. This is indicated by a negative sign in the emf equation. This phenomenon is called Lenz law.

No, Wrong.
Skin depth is found in pure conductors. It the property of the conductor to allow a small amount of electromagnetic energy into its skin, but not completely. This is the reason why EM waves cannot travel inside a good conductor.

No, Wrong.
There are many techniques employed to achieve zero attenuation or maximum propagation. But it is not achievable practically. Thus lossless propagation is not possible practically.

No, Wrong.
The intrinsic impedance is the impedance of a particular material. It is the ratio of square root of the permeability to permittivity. For air, the intrinsic impedance is 377 ohm or 120π.

No, Wrong.
The attenuation is the loss of power of the wave during its propagation. In a lossless dielectric, the loss of power will not occur. Thus the attenuation will be zero.

No, Wrong.
The conductivity will be minimum for a dielectric. For a perfect dielectric, the conductivity will be zero.

No, Wrong.
In distributed lines, the primary parameters are distributed along the circuit with each elemental length having its own values and the concentration of the individual parameters is not possible. An example is the transmission of power.

No, Wrong.
The networks in which the R, L, C parameters are individually concentrated or lumped at discrete points in the circuit are called lumped networks. These networks can be identified definitely as representing a particular parameter. An example is the filters.

No, Wrong.
The primary parameters of a transmission line are the resistance, inductance, capacitance and conductance. The attenuation, phase and propagation constant are secondary parameters. Thus the odd one out is the attenuation constant.

No, Wrong.
The shorted line will absorb more power than any other line. Thus the reflection coefficient is considered to be negative.

No, Wrong.
The skin depth is the measure of the depth to which the amplitude of an EM wave will reduce to 36.8% of its initial value. Thus it can be calculated if the initial amplitude is known.

No, Wrong. The depth to which the electromagnetic waves pass through the conductor is very small. It is measured in μm.

Yes, Correct. The skin of the conductor allows a certain amount of electromagnetic power to pass through it. This phenomenon is called the skin effect. This is the reason why, electromagnetic waves cannot travel inside a conductor.