ENG2031 ENGINEERING ELECTROMAGNETICS 2 2022
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Degrees of MEng, BEng, MSc and BSc in Engineering
ENGINEEtING ELECTtOMAGNETICS 2
(ENG2031)
Thursday 5th May 2022
Release time: 9:30AM (BST)
Exam duration: 2 hours to complete exam plus 30 mins to upload submission.
Attempt ALL questions
Section A (50 marks): Q1 and Q2 (25 marks per question)
Section B (30 marks): Q3 and Q4 (15 marks per question)
Section c (20 marks): Multiple choice (Moodle Quiz) Q5-Q9 (4 marks per question)
The numbeTs in squaTe bTacKets in the Tight-hand maTgin indicate the maTKs allotted to the paTt of the question against which the maTK is shown. These maTKs aTe foT guidance onlg.
DATA SHEET IS PtOVIDED AT THE END OF PAPEt
A calculator may be used. show intermediate steps in calculations.
SECTION A
Q1 consider three elements (P1 , P2 , and P3 ) of negligible section and located at the vertices of a right-angled triangle of legs length a as shown in Figure Q1 (section of the problem at ixed z). The elements cannot move.
(a) suppose that P1 , P2 , and P3 are point charges of charge q1 = q , q2 =(2 q, and q3 = q. ield E(y) at the coordinate of P3 as a function of the problem parameters (q and a) and the constant ε0 . [6]
(a.2) Find the expressions for the magnitude and the angle with the ① axis of the force F(y) acting on P3 as a function of the problem parameters (q and a) and the constant ε0 . [6]
(b) suppose that P1 , P2 , and P3 are ininite conductive wires extending into the z direction, of negligible section and carrying currents I1 = I , I2 = 2 I , I3 = I, directed in the positive z direction. ield B(y) at the coordinate of P3 as a function of the problem parameters (I and a) and the constant μ0 . [6]
(b.2) Find the expressions for the magnitude and the angle with the ① axis of the force per unit length f(y) acting on P3 as a function of the problem parameters (I and a) and the constant μ0 . [7]
Q2 consider a coaxial cable consisting of a cylindrical conductive element of ra- dius R1 surrounded by a cylindrical conductive shell of internal radius R2 and external radius R3 , as shown in Figure Q2 (section of the coaxial cable in a plane orthogonal to the z direction). Assume the inner cylinder carries a current I, directed along the positive z direction, uniformly distributed inside the conductor. Assume that also the outer conductive shell carries a current I, directed along the negative z direction, uniformly distributed inside the conductor.
Derive the expression for the magnitude of the magnetic ield in the plane orthogonal to the z direction as a function of the problem parameters (I , R1 , R2 , R3 ), the distance from the coaxial cable axis (T), and μ0 . speciically compute:
(a) B(r) for (r < R1) [8]
(b) B(T) for (R1 < T < R2 ) [5]
(c) B(T) for (R2 < T < R3 ) [8]
(d) B(T) for (T > R3 ) [4]
SECTION B
Q3 |
compare the electric ield of an electric dipole with the electric ield of a point charge. To this end consider the dipole approximation and: (a) Draw the the electric ield lines for the point charge and for the dipole. (b) Briely describe the main diferences between the electric ield of a point charge and that of a dipole. Mention in your anwer the diferent dependence of the ield strength with the distance. |
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[5] |
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[5] |
(c) Using the appropriate formalism, derive the expression for the electric field of a dipole starting from the superposition principle of the scalar potential (consider the dipole approximation). suggestion. check at the end of the exam paper for the deinition of the gradient operator in spherical coordinates. [5]
Q4 |
consider a region of space with a charge density p(T) which is constantin time. (a) show that it can be permeated by an electric ield of the form: where p = , TO is a constant measured in meters, and A, B are constants with units to be determined. suggestion: check at the end of the exam paper for useful expressions of vectorial operations in spherical coordinates and demonstrate that the given ield satisies Maxwell,s equations. (b) state the units of A and B . (c) state the expression of the charge density p(T) distributed in the region of space as a function of the problem parameters B and TO , the radial coordinate T , and the constant εO . |
[3]
[4] |
2023-08-02