This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Maxwell Law 4”.
1. Which quantity is solenoidal in the electromagnetic theory?
a) Electric field intensity
b) Electric flux density
c) Magnetic field intensity
d) Magnetic flux density
Explanation: The divergence of the magnetic flux density is zero. This is the Maxwell fourth equation. As the divergence is zero, the quantity will be solenoidal or divergent less.
2. Which equation will be true, if the medium is considered to be air?
a) Curl(H) = 0
b) Div(H) = 0
c) Grad(H) = 0
d) Div(H) = 1
Explanation: From the Gauss law for magnetic field, the divergence of the magnetic flux density is zero. Also B = μH. Thus divergence of H is also zero, i.e, Div(H) = 0 is true.
3. Find the sequence to find B when E is given.
Explanation: From E, D can be computed as D = εE. Using the Ampere law, H can be computed from D. Finally, B can be calculated from H by B = μH.
4. The Gauss law for magnetic field is valid in
d) All cases
Explanation: The Gauss law for magnetic field states that the divergence of B is always zero. This is valid for all cases like free space, dielectric medium etc.
5. The sequence for finding H from E is
Explanation: From E, we can compute B using the Maxwell first law. Using B, the parameter H can be found since B = μH. Thus the sequence is E-B-H is true.
6. The reason for non existence of magnetic monopoles is
a) The magnetic field cannot be split
b) Due to permeability
c) Due to magnetization
d) Due to magnetostriction
Explanation: Practically monopoles do not exist, due to the connection between north and south poles. But theoretically, they exist. The reason for their non- existence practically is that, the magnetic field confined to two poles cannot be split or confined to a single pole.
7. The non existence of the magnetic monopole is due to which operation?
Explanation: The Maxwell fourth law or the Gauss law for magnetic field states that the divergence of B is zero, implies the non existence of magnetic monopoles. Thus the operation involved is divergence.
8. Will dielectric breakdown lead to formation of magnetic monopole?
Explanation: When dielectric breakdown occurs, the material loses its dielectric property and becomes a conductor. When it is subjected to a magnetic field, north and south flux lines coexists, giving magnetic force. Thus there exists magnetic dipole. Suppose if the conductor is broken into very small pieces, still there exist a magnetic dipole in every broken part. In other words, when a piece is broken into half, there cannot exist a north pole in one half and a south pole in the other. Thus monopoles never exist.
9. Which equation will hold good for a magnetic material?
a) Line integral of H is zero
b) Surface integral of H is zero
c) Line integral of B is zero
d) Surface integral of B is zero
Explanation: We know that the divergence of B is zero. From Stokes theorem, the surface integral of B is equal to the volume integral of divergence of B. Thus surface integral of B is also zero.
10. The dipole formation in a magnet is due to
a) Interaction between the north and south poles together
b) Interaction between the north pole with the air
c) Interaction between the south pole with the air
d) Interaction of north and south pole separately with air
Explanation: In any magnetic material or magnet, the dipoles exist. This is due to the magnetic lines of force joining the north to south poles. The interaction between these two poles together leads to dipole formation.
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