This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Magnetic Dipole”.
1. The magnetic moment of a field with current 12A and area 1.6 units is
Explanation: The magnetic moment is the product of current and the area of the conductor. It is given by M = IA, where I = 12 and A = 1.6.Thus we get, M = 12 x 1.6 = 19.2 units.
2. Find the torque of a loop with magnetic moment 12.5 and magnetic flux density 7.65 units is
Explanation: The torque is defined as the product of the magnetic moment and the magnetic flux density given by T = MB, where M = 12.5 and B = 7.65. Thus we get T = 12.5 x 7.65 = 95.625 units.
3. The magnetization is defined by the ratio of
a) Magnetic moment to area
b) Magnetic moment to volume
c) Magnetic flux density to area
d) Magnetic flux density to volume
Explanation: The magnetization refers to the amount of dipole formation in a given volume when it is subjected to a magnetic field. It is given by the ratio of the magnetic moment to the volume. Thus Pm = M/V.
4. Find the orbital dipole moment in a field of dipoles of radius 20cm and angular velocity of 2m/s(in 10-22 order)
Explanation: The orbital dipole moment is given by M = 0.5 x eVangx r2, where e = 1.6 x 10-19 is the charge of the electron, Vang = 2 and r = 0.2. On substituting, we get M = 0.5 x 1.6 x 10-19x 2 x 0.22= 64 x 10-22 units.
5. Find the orbital angular moment of a dipole with angular velocity of 1.6m/s and radius 35cm(in 10-31 order)
Explanation: The orbital angular moment is given by Ma = m x Vangx r2,where m = 9.1 x 10-31, Vang = 1.6 and r = 0.35. On substituting, we get, Ma = 9.1 x 10-31 x 1.6 x 0.352 = 1.78 x 10-31 units.
6. The ratio of the orbital dipole moment to the orbital angular moment is given by
Explanation: The orbital dipole moment is given by M = 0.5 x eVangx r2 and the orbital angular moment is given by Ma = m x Vangx r2. Their ratio M/Ma is given by –e/2m, the negative sign indicates the charge of electron.
7. Calculate the Larmer angular frequency for a magnetic flux density of 12.34 x 10-10.
Explanation: The Larmer angular frequency is the product of magnitude of the ratio of orbital dipole moment to orbital angular moment and the magnetic flux density. It is given by fL = B e/2m, where is the charge of electron and m is the mass of the electron. On substituting, we get fL = 12.34 x 10-10 x 1.6 x 10-19/(2 x 9.1 x 10-31) = 108.36 units.
8. The Bohr magneton is given by
Explanation: In atomic physics, the Bohr magneton (symbol μB) is a physical constant and the natural unit for expressing the magnetic moment of an electron caused by either its orbital or spin angular momentum. It is given by eh/4πm, where h is the Planck’s constant, e is the charge of the electron and m is the mass of the electron.
9. Find the magnetization of the field which has a magnetic moment 16 units in a volume of 1.2 units.
Explanation: The magnetization is the ratio of the magnetic moment to the volume. Thus M = m/v, where m = 16 and v = 1.2. We get M = 16/1.2 = 13.33 units.
10. Which of the following is true regarding magnetic lines of force?
c) Does not exist
d) Parallel to field
Explanation: Magnetic Lines of Force is a an imaginary line representing the direction of magnetic field such that the tangent at any point is the direction of the field vector at that point.
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