This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Magnetostatic Properties”.
1. The magnetostatics highly relies on which property?
Explanation: The magnetostatics highly relies on the inductance of the magnetic materials, which decides its behavior in the influence of magnetic field.
2. The inductance is the measure of
a) Electric charges stored by the material
b) Emf generated by energising the coil
c) Magnetic field stored by the material
d) Magnetization of dipoles
Explanation: The inductance is a property of an electric conductor/coil which measures the amount of emf generated by passing current through the coil.
3. Find the total flux in a coil of magnetic flux density 12 units and area 7 units.
Explanation: The total flux in a coil is defined by φ = BA, where B = 12 and A = 0.07. On substituting these values, we get φ = 12 x 0.07 = 0.84 units.
4. Find the energy of a coil of inductance 18mH and current passing through it 1.25A.(in 10-3 order)
Explanation: The magnetic energy possessed by a coil is given by E = 0.5 x LI2. Put L = 18 x 10-3 and I = 1.25, thus we get E = 0.5 x 18 x 10-3 x 1.252 = 14.06 x 10-3 units.
5. Using Maxwell equation which of the following cannot be calculated directly?
Explanation: The Maxwell equations can be used to compute E,H,D,B and J directly. It is not possible to find the magnetic vector potential A directly.
6. Which of the following relation will hold good?
a) D = μ H
b) B = ε E
c) E = ε D
d) B = μ H
Explanation: The magnetic flux density is the product the permeability and the magnetic field intensity. This statement is always true for any material (permeability).
7. The permeability and permittivity of air or free space is unity. State true/false.
Explanation: The permeability and permittivity of free space or air is always unity. This implies that the air is always ready to store electric or magnetic charges subjected to it.
8. Choose the best relation.
a) A = -Div(V)
b) V = Curl(A)
c) H = -Grad(V)
d) V = Div(E)
Explanation: For any magnetic field, the magnetic field intensity will be the negative gradient of the potential of the field. This is given by H = -Grad(V).
9. Find the magnetic field when the magnetic vector potential is a unit vector.
Explanation: We know that H = -Grad(V), where is a unit vector. The gradient of a constant/unit vector will be zero. Thus the magnetic field intensity will be zero.
10. Find the force experienced by an electromagnetic wave in a conductor?
a) Electrostatic force
b) Magneto static force
c) Electro motive force
d) Lorentz force
Explanation: The electromagnetic wave experiences Lorentz force which is the combination of the electrostatic force and magneto static force. It is given by F = QE + Q(V X B).
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