Q.1. Define Electromagnetics?
Answer: Electromagnetics is a branch of physics or electrical engineering which is used to study the electric and magnetic phenomenon. The electric and magnetic fields are closely related to each other.
Q.2. What is the difference between the scalar and vector?
Answer: A scalar is a quantity which is wholly characterized by its magnitude. The various example of scalar quantity are temperature, mass, volume, density, speed, electric charge etc. A vector is a quantity which is characterized by both magnitude and direction. The various examples of vector quantity are force, velocity, displacement, electric field intensity, magnetic field intensity, acceleration etc.
Q.3. Define scalar or dot product of vector.
Answer: The scalar or dot product of two vectors A and B is denoted as A.B and defined as the product of the magnitude of A, the magnitude of B and the cosine of the smaller angle between them.
Q.4. Define vector or cross product of vectors.
Answer: The vector or cross product of two vectors A and B is denoted as AXB and defined as the product of the magnitude of A and B and the sine of the smaller angle between A and B.
Q.5. How two vectors behave if their dot product is zero?
Answer: If dot product of the two vectors is zero, the two vectors are perpendicular to each other.
Q.6. How two vectors behave if their cross product is zero?
Answer: If cross product of the two vectors is zero, the two vectors are parallel to each other.
Q.7. State Divergence theorem.
Answer: The integral of the normal component of any vector field over a closed surface is equal to the integral of the divergence of this vector field throughout the volume enclosed by the closed surface.
Q.8. Define Curl of a vector.
Answer: Curl is simply defined as circulation per unit area where the closed path is vanishingly small. That is curl is defined at a point.
Q.9. State Stokes theorem.
Answer: It states that the circulation of a vector field A around a closed path C is equal to the surface integral of the curl of A over the open surface ‘S’ bounded by ‘C’ provided that A and curl of A are continuous on ‘S’.
Q.10. What is the use of divergence and curl operations?
Answer: Divergence and curl are the operations used to check the nature of field whether it is solenoidal or irrotational. A vector is said to be solenoidal when divergence of a vector is zero whereas a vector is said to be irrotational when curl of a vector is zero.
Q.11. State coulomb’s law.
Answer: Coulomb stated that the force between two very small charges separated in a vacuum or free space by a distance r (which is large compared to the size of the charge) is proportional to the multiplication of charges and inversely proportional to the square of the distance between them.
Q.12. What do you mean by harmonic field?
Answer: A scalar field is said to be harmonic in a given region, if its laplacian vanishes in that region.
Q.13. State Gauss’s law for electric field.
Answer: It states that the electric flux passing through any closed surface is equal to the total charge enclosed by that surface.
Q.14. In case of co-axial cable, what is the value of the electric field at the core of the cable and outside the conductor?
Answer: Both at the core of the cable and outside the conductor, the electric field is zero.
Q.15. What is an electric dipole?
Answer: An electric dipole is the arrangement of two point charges of equal magnitude and opposite sign, separated by a distance which is small compared to the distance of point ‘P’ at which we desire the electric field and potential. It is also called as doublet.
Q.16. What is drift velocity and how it relates to the electric field intensity?
Answer: In free space the electrons would accelerate and their velocity continuously increases in the material. The progress of the electron is hindered by regular collisions with the thermally excited crystalline lattice structure and a constant average velocity is soon attained. This velocity is known as drift velocity and it is directly proportional to electric field intensity in the given material.
Q.17. What do you mean by homogeneous medium?
Answer: A medium is homogeneous, if its physical characteristics (mass, density, molecular structure etc) do not vary from point to point. If the medium is not homogeneous, it is aid to be non-homogeneous or inhomogeneous or heterogeneous.
Q.18. What is isotropic material?
Answer: An isotropic material is one whose properties are independent of direction. The materials whose molecular structure is randomly oriented will be isotropic. However, crystalline media or certain plasma has directional characteristics. Such materials are said to be non-isotropic and anistropic.
Q.19. What do you mean by polarization?
Answer: Polarization is the creation of net charge in presence of electric field. Polarization ‘P’ is defined as total dipole moment per unit volume.
Q.20. What will be the work done in moving the charge around any closed loop?
Answer: The work done in moving the charge around any closed loop is zero.
Q.21. What do you mean by equipotential surfaces?
Answer: All the point in space at which the potential has the same value lie on a surface is called as equipotential surface or simply equipotential.
Q.22. How we can obtain quadrupole with the help of dipoles?
Answer: Placing two dipoles adjacent but with one inverted, we obtain a quadrupole and placing two quadrupoles side by side but with one inverted, we obtain an octopole.
Q.23. How potential and field of a quadrupole and octopole varies with respect to ‘r’?
Answer: The potential and field of a quadrupole vary as 1/r3 and 1/r4 respectively and for an octopole as 1/r4 and 1/r5.
Q.24. What are linear materials?
Answer: If the parameters of the material do not depend on the magnitude of the field quantities then the material is linear. A ferroelectric or ferromagnetic material is non linear because its electrical or magnetic properties depend on the strength of the applied field.
Q.25. What do you mean by convection current and conduction current?
Answer: Convection current-
- It does not involve conductors.
- So does not satisfy ohm’s law.
- This current flow through an insulating medium such as liquid, rarefied gas or a vacuum.
- Well known example is a vacuum tube in which electrons emitted by cathode flows to anode in a vacuum.
Conduction current-
- It requires conductor.
- It satisfies ohm’s law.
- Current through any conductor is of this type.
Q.26. Explain relaxation time with an example?
Answer: Imagine that you have a solid metal ball or sphere and you place a charge inside of it. This charge will arrive at the surface as a surface charge. How fast this charge arrives at the surface can be calculated using the term relaxation time.
Q.27. What are the properties of perfect conductor?
Answer: The properties of perfect conductor are –
- Within a conductor, charge or charge density is zero and a surface charge density is present on the outer surface of the conductor.
- The electric field intensity within the conductor is zero.
- The tangential component of external electric field intensity as well as electric flux density is zero.
- The conductor surface is an equipotential surface.
- The normal component of electric flux density is equal to surface charge density on the conductor surface.
Q.28. What do you mean by boundary conditions?
Answer: The conditions existing at the boundary of the two media when field passes from one medium to other are called boundary conditions. Depending upon the nature of the media, there are two situations of the boundary conditions. Boundary between conductor and free space or boundary between conductor and dielectric. Boundary between two dielectrics with different properties.
Q.29. Who discovered the relation between electric and magnetic fields?
Answer: The scientist oersted has discovered the relation between electric and magnetic fields in 1820.
Q.30. What do you mean by magnetostatics?
Answer: The study of steady magnetic field, existing in a given space, produced due to the flow of direct current through a conductor is called magnetostatics.
Q.31. Which thumb rule is used to determine the direction of magnetic field around a conductor carrying a direct current?
Answer: Right hand thumb rule. It states that, hold the current carrying conductor in the right hand such that thumb pointing in the direction of current and parallel to the conductor, then curled fingers point in the direction of the magnetic lines of flux around it.
Q.32. State Biot-Savart law?
Answer: It states that, the magnetic field intensity dH produced at a point ‘P’ due to a differential current element IdL is,
- Proportional to the product of the current I and differential length dL.
- The sine of the angle between the element and the line joining point ‘P’ to the element.
- And inversely proportional to the square of the distance R between point P and the element.
Q.33.State Ampere’s Circuital law.
Answer: It states that, the line integral of magnetic field intensity ‘H’ around a closed path is exactly equal to the direct current enclosed by that path.
Q.34. How we can say whether the field is rotational or irrotational?
Answer: If curl of a vector field exists then the field is called rotational. For irrotational vector field, the curl vanishes i.e. curl is zero.
Q.35. What is the value of the divergence of the magnetic flux density?
Answer: The divergence of magnetic flux density is always zero. This is called Gauss’s law in differential form for magnetic fields.
Q.36. What do you mean by the magnetic dipole moment of a current loop?
Answer: The magnetic dipole moment of a current loop is defined as the product of current through the loop and the area of the loop, directed normal to the current loop. From the definition it is clear that, the magnetic dipole moment is a vector quantity.
Q.37. What are the different classification of magnetic materials?
Answer: On the basis of the magnetic behavior, the magnetic materials are classified as diamagnetic, paramagnetic, ferromagnetic, antiferomagnetic, ferimagnetic and supermagnetic
Q.38. What are diamagnetic materials?
Answer: The magnetic materials in which the orbital magnetic moment and electron spin magnetic moment cancel each other making net permanent magnetic moment of each atom zero are called diamagnetic materials.
Q.39. What are paramagnetic materials?
Answer: The magnetic materials in which the orbital and spin magnetic moments do not cancel each other resulting in a net magnetic moment of an atom are called as paramagnetic materials.
Q.40. What are ferromagnetic materials?
Answer: The materials in which the atoms have large dipole moment due to electron spin magnetic moments are called ferromagnetic materials.
Q.41. What are anti ferromagnetic materials?
Answer: The materials in which the dipole moments of adjacent atoms line up in antiparallel fashion are called anti ferromagnetic materials.
Q.42. What are ferimagnetic materials?
Answer: The materials in which the magnetic dipole moments are lined up in antiparallel fashion, but the net magnetic moment is non-zero are called ferimagnetic materials.
Q.43. What are supermagnetic materials?
Answer: In supermagnetic materials, the ferromagnetic materials are suspended in the dielectric matrix. The important property of the supermagnetic material is that even though each particle of it contains large magnetic domains but cannot penetrate adjacent particles.
Q.44. What do you mean by domains?
Answer: The region in which large number of magnetic moments lined in parallel are called domains.
Q.45. What is Kirchhoff’s flux law?
Answer: Kirchhoff’s flux law states that the total magnetic flux arriving at any junction in a magnetic circuit is equal to the total magnetic flux leaving that junction.
Q.46. Which current (conduction current or displacement current) is larger in conductor and in dielectric medium?
Answer: In conductor, the conduction current is very large as compared to the displacement current whereas in dielectric medium, the displacement current is greater as compared to the conduction current.
Q.47. Define uniform plane wave.
Answer: A plane electromagnetic wave is defined as a wave in which both the electric (E) and magnetic (H) vectors are at right angles to the direction of propagation. At any instant of time, both vectors have the same magnitude and direction at all points in the transverse plane which contains them.
Q.48. What is skin depth or depth of penetration?
Answer: The distance through which the amplitude of the travelling wave decreases to 37% of the original amplitude is called skin depth or depth of penetration.
Q.49. When the polarization is said to be linear?
Answer: When Ex and Ey components are in phase with either equal or unequal amplitudes, for a uniform plane wave travelling in Z-direction, the polarization is linear.
Q.50. When the polarization is said to be elliptical?
Answer: When the components Ex and Ey of unequal amplitudes have a constant, non-zero phase difference between two, for a uniform plane wave travelling in Z-direction, the polarization is elliptical.