1 | P a g e
Electrical Engineering Department Electromagnetics I (802323) – G1
Dr. Mouaaz Nahas
Term 2 (1437-1438)
Final Exam (50% of the Total Mark) Thursday 18/05/2017 (22/8/1438 H)
:مسلاا __________________________________________
لا :يعماجلا مقر ____________________________
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CLO #: CLO: Mark:
CLO 2 Calculate both Electric and Magnetic Field Intensities and Flux densities for different
configurations. 20
Q1. Choose the correct answer:
1. The vector field E is called:
a) The electric flux density b) The electric field intensity c) The electric field density d) The electric flux intensity 2. The vector D is measured in:
a) C/m b) V/m
c) C/N d) C/m2
3. The electric force between any two point charges (with distance R) is calculated as:
a) F = aR (Q1Q2) / (4πεR) b) F = R (Q1Q2) / (4πεR3) c) F = aR (Q1Q2) / (4πεR2) d) b) and c)
4. Which of the following is not a true form of Gauss’s law?
a)
D . dS = Qenc b)
D . dS =
v vdv
c)
v vdv
= Ψ d) . E =
v5. Given the potential field 𝑉 = 𝑥2𝑦𝑧. At point (1, 1, 0), which statement is correct?
a) E and V vanish b) E vanishes but V does not a) E and V do not vanish c) V vanishes but E does not 6. Equipotential line means that potential V:
a) Is a function of only x or y or z b) Is not constant across the whole line c) Is constant across the whole line d) None of the above
7. Two infinite filamentary lines carry the same current I but in opposite directions. If H is the magnetic field produced by one line, the field at a point located in the midway between the two lines equals:
a) 0 b) H
c) 2H d) H/2
50
2 | P a g e 8. Which configuration is not a correct representation of I and H?
a) b)
c) d)
9. The two bar magnets 1 and 2 shown in the figure have magnetic charges of 20 A.m. The total magnetic flux leaving the volume (in Wb) is:
a) 0 b) 20
c) 40 d) Need more data to calculate it
10. The z-axis carries filamentary current of 10π A along az. H at P(0, 5, 0) equals:
a) ax A/m b) – ax A/m
c) – aφ A/m d) – 0.8 ax – 0.6 ay A/m
11. Plane y = 0 carries a uniform current of 2 az A/m. H at P(1, 10, –2) is calculated as:
a) az × ay (A/m) b) – az × ay (A/m) c) az × ax (A/m) d) – az × ax (A/m) 12. For the current and closed path shown, the value of
L
H . dl equals:
a) 20 A b) – 20 A
c) 0 A d) 40 A
13. Based on Ampere’s law, which one of the following will give zero line integral of H?
a) b)
c) d)
14. In magnetostatic fields, which one is not a characteristic of H?
a) H is solenoidal b) H is conservative (irrotational) c) H is divergenceless d) Magnetic flux lines are always closed
3 | P a g e 15. The magnetic vector potential A is measured in:
a) Wb b) Wb/m
c) Wb/m2 d) Wb.m
16. Given a conducting wire of radius R, the magnitude of H inside the wire equals:
a) 𝐼
2𝜋𝜌 b) 𝐼
2𝜋𝜌2
c) 𝜌𝐼
2𝜋𝑅2 d) 𝜌𝐼
2𝜋𝑅
17. Which formula can be used to calculate the magnetic flux 𝛹?
a)
L
A . dl b)
S
B . dS c)
S
(𝛁 × A) . dS d) All the above
18. Given A = – ρ/4 az. The total magnetic flux 𝛹 crossing the surface ϕ = π/2, 1 ≤ ρ ≤ 2 m, 0 ≤ z ≤ 5 m equals:
a) 3.75 Wb b) 2.5 Wb
c) 1.25 Wb d) 0 Wb
19. In the previous question, if A is uniform, the magnetic flux 𝛹 crossing the same surface equals:
a) 3.75 Wb b) 2.5 Wb
c) 1.25 Wb d) 0 Wb
20. Which one is not a source of magnetostatic fields?
a) A dc current in a wire b) A permanent magnet
c) An electric field linearly changing with time d) A rotating charged disk with constant speed CLO 3 Apply Laplace’s and Poisson’s equations on simple configurations.
5 Q2. Choose the correct answer:
21. Which of the following potentials does not satisfy Laplace's equation?
a) V
2
x5
b) V 10xyc) V 10r
d) V 3z2
22. Laplace’s and Poisson’s equations are used to find E if we know:
a) The electric potential V b) The charge distribution
c) The electric flux density d) Only some boundary conditions 23. Laplace’s equation is a special case of Poisson’s equation when we have:
a) Free space medium b) Free charge region
c) Volume charge density d) All the above
24. In free space, V = 6 x y2 z + 8. Find E at P(1, 2, –5),:
a) (–120, 120, –24) V/m b) (120, 120, –24) V/m
c) (120, 120, 24) V/m d) More information is needed to find E
4 | P a g e 25. In the previous question, the volume charge density at P (in C/m3) equals:
a) 60 b) – 60
c) 60 εo d) – 60 εo
CLO 4 Solve the formulas of the forces and torques due to magnetic field in different
configurations. 5
Q3. Choose the correct answer:
26. For a stationary charge Q, the total (electric and magnetic) force is calculated as:
a) Q u b) Q u × B
c) Q E d) Q (u × B + E)
27. For a charge Q moving with a velocity u in a magnetic field, the total force is calculated as:
a) Q u b) Q u × B
c) Q E d) Q (u × B + E)
28. Which one represents Lorentz force law?
a) Q u b) Q u × B
c) Q E d) Q (u × B + E)
29. The force on differential length dl at point P in the conducting circular loop shown is:
Recall: F =
L
I dl × B
a) Outward along OP b) Inward along OP
c) In the direction of B d) Tangential to the loop at P
30. A charge particle of mas 2 kg and charge 3 C moves with velocity 4ax + 3az m/s in an electric field E = 12 ax + 10 ay V/m. The acceleration a (in m/s2) equals:
Recall: F = m a
a) (6, 5, 0) b) (6, 0, 4.5)
c) (2, 0, 1.5) d) (18, 15, 0)
CLO 5 Calculate the induced voltage for time varying electromagnetic fields.
5 Q4. Choose the correct answer:
31. For a circuit with N-turns, which one represents the Faraday’s law?
a) Vemf = N dλ / dt b) Vemf = – dψ / dt
c) Vemf = dλ / dt d) b) and c)
32. The flux through each turn of a 100-turn coil is (t3 – 2t) mWb, where t is in second. The induced electromotive force at t = 2 is:
a) 1 V b) – 1 V
c) 0.4 V d) – 0.4 V
33. Galvanometer is a device that measures:
a) Current induced by constant flux b) Current induced by time-varying flux c) Voltage induced by constant flux d) Voltage induced by time-varying flux
5 | P a g e 34. In the figure shown, the emf is measured between:
a) A and B b) C and D
c) E and F d) G and H
35. If B = – 0.3t az , Vemf and V1 equal (in Volt):
a) Vemf = 1.2t and V1 = 0.4 b) Vemf = 1.2 and V1 = 0.4 c) Vemf = 1.2t and V1 = 0.8 d) Vemf = 1.2 and V1 = 0.8
CLO 6 Concepts and practical meaning of Maxwell’s equations (Faraday’s law, Ampere’s law,
Gauss’s law and conservation of charge). 10
Q5. Choose the correct answer:
36. In the third Maxwell’s equation, the term 𝜕D/𝜕t is called:
a)
Conduction current densityb)
Ampere’s current densityc)
Displacement current densityd)
Surface current density 37. Which of the following fields is not Maxwellian (or nonexistent)?a) E = 50 cos (t – 10) ax b) E = (1 – ρ) sin t aφ
c) E = 10 cos t cos r aθ d) E = 50 cos yt ay
38. Given a non Maxwellian field E = sin t ax. To make E Maxwellian, it should be modified as:
a) E = sin (t – 50) ax b) E = sin (t – 50x) ax
c) E = sin (t – 50z) ax d) b) and c) 39. For time-varying fields, which of the following is true?
a) E and H are independent of each other b) E and H are dependent of each other c) E and D are independent of each other d) B and H are independent of each other 40. In free-space, given E = 20 cos (ωt – 50x) ay V/m. Jd is calculated as:
a) 𝜀𝑜𝜕𝐄
𝜕𝑡 b) 𝜕𝐄
𝜕𝑡 c) 𝜀𝑜𝜕𝐄
𝜕𝑥 d) 𝜕𝐄
𝜕𝑥 41. In the previous question, to calculate H from E, we can use:
a) 1st Maxwell’s equation b) 2nd Maxwell’s equation c) 3rd Maxwell’s equation d) b) and c)
6 | P a g e 42. Comparing with static fields, which Maxwell’s equations are modified in time-varying fields:
a) 1st and 2nd b) 2nd and 3rd
c) 3rd and 4th d) 1st and 3rd
43. The vector J is called:
a) Conduction current density b) Displacement current density
c) Volume current density d) a) and c)
44. Which of the following is always true?
a) × E = 0 b) . D = 0
c) × H = 0 d) . B = 0
45. For the shown configuration, where S2 is a surface bounded by the Amperean’s path L, which equation satisfies Ampere’s law:
a)
L
H . dl = 0 b)
L
H . dl = I c)
L
H . dl = Id d) × H = J
CLO 7
Apply knowledge about the importance and the application of Electromagnetic in electrical engineering (communication, electronics, computer, radar, electrical
machines, transformer, cables and power transmission system). 5 Q6. Choose the correct answer:
46. Which one is a Magnetostatic field application?
a) DC motor b) Radio waves
c) AC motor d) All the above
47. Radio wave is an application of:
a) Electrostatic field b) Magnetostatic field
c) Electromagnetic fields d) All the above
48. Based on EM theory, the current between the two plates in a capacitor flows through:
a) Movement of charges in the dielectric b) Movement of charges in the plates c) Rate of change of electric field between the
plates
d) Rate of change of magnetic field between the plates
49. Optical fibers are applications of EM theory in the area of:
a) Electronics engineering b) Power engineering c) Communication engineering d) None of the above 50. In electromagnetics, should we focus on infinite current lines? Why?
a) No, because infinite current lines never exist b) Yes, because most current lines are infinite c) No, because most current lines are finite d) Yes, because most current lines are relatively
too long
