This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Magnetic Field Density”.
1. Identify which of the following is the unit of magnetic flux density?
Explanation: The unit of magnetic flux density is weber/m2. It is also called as tesla.
2. The divergence of H will be
Explanation: We know that the divergence of B is zero. Also B = μH. Thus divergence of H is also zero.
3. Find the flux contained by the material when the flux density is 11.7 Tesla and the area is 2 units.
Explanation: The total flux is given by φ = ∫ B.ds, where ∫ds is the area. Thus φ = BA. We get φ = 11.7 x 2 = 23.4 units.
4. Find the current when the magnetic field intensity is given by 2L and L varies as 0->1.
Explanation: From Ampere law, we get ∫ H.dL = I. Put H = 2L and L = 0->1. On integrating H with respect to L, the current will be 1A.
5. Find the magnetic field intensity when the flux density is 8 x 10-6 Tesla in the medium of air.
Explanation: We how that, B = μH. To get H = B/μ, put B = 8 x 10-6 and μ = 4π x 10-7. Thus H = 8 x 10-6/ 4π x 10-7 = 6.36 units.
6. If ∫ H.dL = 0, then which statement will be true?
a) E = -Grad(V)
b) B = -Grad(D)
c) H = -Grad(Vm)
d) D = -Grad(A)
Explanation: The given condition shows that the magnetic field intensity will be the negative gradient of the magnetic vector potential.
7. Find the magnetic flux density of the material with magnetic vector potential A = y i + z j + x k.
a) i + j + k
b) –i – j – k
Explanation: The magnetic flux density is the curl of the magnetic vector potential. B = Curl(A). Thus Curl(A) = i(-1) – j(1) + k(-1) = -i – j – k. We get B = -i – j – k.
8. Find the magnetic flux density when a flux of 28 units is enclosed in an area of 15cm.
Explanation: The total flux is the product of the magnetic flux density and the area. Total flux = B x A. To get B, put flux/area. B = 28/0.15 = 186.67 units.
9. Find the magnetic flux density B when E is given by 3sin y i + 4cos z j + ex k.
a) ∫(4sin z i – ex j – 3cos y k)dt
b) -∫(4sin z i – ex j – 3cos y k)dt
c) ∫(4sin y i – ex j + 3cos y k)dt
d) -∫(4sin y i + ex j + 3cos y k)dt
Explanation: We know that Curl (E) = -dB/dt. The curl of E is (4sin z i – ex j – 3cos y k). To get B, integrate the -curl(E) with respect to time to get B = -∫(4sin z i – ex j – 3cos y k)dt.
10. Find current density J when B = 50 x 10-6 units and area dS is 4 units.
Explanation: To get H, H = B/μ = 50 x 10-6/ 4π x 10-7 = 39.78 units. Also H = ∫ J.dS, where H = 39.78 and ∫ dS = 4. Thus J = 39.78/4 = 9.94 units.
Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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