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Code No: NR210204

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II B.Tech I Semester Supplimentary Examinations, May/Jun 2009 ELECTROMAGNETIC FIELDS (Electrical & Electronic Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) State and explain Coulomb’s law

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(b) Two small identical conducting spheres have charges of 2nC and ?0.5nC respectively. When they are placed 4 cm apart what is the force between them. If they are brought into contact and then separated by 4cms what is the force between them? [8]

2. (a) If a sphere of radius ‘a’ has a charge density ρ = kr3 Find D and ∇.D as a function of radius and sketch the results. k is a constant. [6]

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(b) A charge Q is uniformly distributed in a half-circular ring of radius ‘a’. Determine E at center. [10]

3. (a) Derive the expression for potential and field between two co-axial cylinders. [8]

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(b) Find the capacitance of parallel plate capacitor when A = 1sq mt distance between the plate 1 mm voltage gradient is 105 V /m and charge density on the plate is 2 µC/m2 . [8] 4. (a) A parallel plate capacitor comprising two square plates,‘L’m on a side, separated by a distance ‘d’m , is connected to a constant d.c.supply.A dielectric slab of width ‘L’m and thickness ‘d’ is inserted between the plates. Neglecting edge effect, find expression for the following. [8]

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i. The total energy stored in the capacitor. ii. The force tending to draw the dielectric slab in to the capacitor. ¯ field within an infinite, homogenous (b) Determine the energy density of an E? and isotropic medium having permitivity ε . [8]

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5. State and prove Ampere’s circuital law. Discuss few applications for the same.[16] 6. A single-phase circuit comprises two parallel conductors A and B, each 1 cm diameter and spaced 1 m apart. The conductors carry current of +100 and -100 Amps. respectively. Determine the filed intensity at the surface of each conductor and also in space exactly midway between A and B. [16] 7. Define and explain the term scalar magnetic potential inside a magnetic field. What is the usefulness of this parameter? State its limitations. How can we determine this quantity as a function of X, Y and Z co-ordinates in space? [16] 8. (a) State and explain the Faraday’s laws in Electro magnetic induction? 1 of 2

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Code No: NR210204

(b) A stationary 10turns square coil of 1-meter side is situated with its lower left corner coincident with the origin and with side’s x1 and y1 along x-axis and y-axis. If the field B is normal to the plane of the coil and has its amplitude sin Πy Tesla. Determine the r.m.s value of e.m.f. induced given by B0 = sin Πx x1 y1 in the coil if B varies harmonically at a frequency of 1 KHz. [10]

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