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Electromagnetic Fields Question Paper - Dec 15 - Electrical And Electronics (Semester 3) - Jawaharlal Nehru Technological University (JNTUH)
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Electromagnetic Fields - Dec 15
Electrical And Electronics (Semester 3)
Total marks: 75
Total time: 3 Hours
Note:-
This question paper contains two parts A and B.
Part A is compulsory which carries 25 marks.
Part B consists of 5 units. Answer any one full question form each unit.
Each question carries 10 marks and may have a,b,c as sub questions.
1.a.
Define electric field intensity. Mention any two sources of electromagnetic field.
(2 marks)
00
1.b.
Give the relation between electric field intensity and electric flux density.
(3 marks)
00
1.3.
Define the boundary conditions for the conductor free space boundary in electrostatic and interface between two dielectrics.
(2 marks)
00
1.d.
What is polarization? Define polarization and write mathematical equations fir polarization.
(3 marks)
00
1.e.
Draw the magnetic field pattern in and around a solenoid.
(2 marks)
00
1.f.
A long straight wire carries a current I=1 amp. At what distance is the magnetic field H=1A/m.
(3 marks)
00
1.g.
Define magnetic dipole moment. Sketch the field due to magnetic dipole.
(2 marks)
00
1.h.
A solenoid has an inductance of 20mH. If the length of the solenoid is increased ny two times and the radius is decreased to half of its original value. Find the new inductance.
(3 marks)
00
1.i.
What is the significance of the Ratio of the magnitude of the conduction current density to the displacement current density?
(2 marks)
00
1.j.
Determine the emf induced obout the path r=0.5 , z=0, t=0 ,. If B=0.01 sin377t.
(3 marks)
00
PART-B
2.a.
Derive an expression for the electric field due to straight and infinite uniformly charged wire of length 'L' meters and with a charge density of a + $\lambda$ cm at a point P which lies along the perpendicular bisector of wire.
(10 marks)
00
OR
3.a.
A circular disc of a radius'a' m is changed uniformly with a charge density of a $\sigma$cm² . Find the electric field at a point'h' m form the disc Along its Axis.
(10 marks)
00
OR
4 .a.
Explain and derive the boundary condition for a conductor free space interface.
(5 marks)
00
4.b
Find the total current in a circular conductor of radius 4mm if the current density varies according to J=(10⁴/r) A/m².
(5 marks)
00
OR
5.a.
Derive the boundary condition of the normal and tangential components of electric field at the interface of two media with different dielectrics.
(5 marks)
00
5.b
Find the capacitance of a conducting sphere of 2cm in Diameter, covered with a layer of polyethylene with $\epsilon$ = 2.26 and 4 cm thick.
(5 marks)
00
6.a.
Derive the magnetic field intensity in the different regions of co-axial cable by applying Ampere's circutial kaw.
(5 marks)
00
6.b.
Derive and expression of magnetic field intensity due to a linear conductor of infinite length carrying current I at a distance., point p. Assume R to be the distance between conductor and point P. Use Biot-savart's Law.
(5 marks)
00
OR
7.
Derive a general expression for the magnetic flux density B at any point along the axis of the long solenoid. Sketch the variation B from point to point along the axis.
(10 marks)
00
8.a.
Calculate the self inductance of infinitely long solenoid.
(5 marks)
00
8.b
A solenoid is 50 cm long, 2 cm in diameter and contains 1500 turns.cylindrical core has a diameter of 2 cm and a relative permeability of 75. This coil is co-axial with a second solenoid, also 50 cm long, but 3 cm diameter and 12 turns. Calculate L for the inner solenoid and L for the outer solenoid.
(5 marks)
00
OR
9.a.
Derive the expression for inductance of a toroidal coil carrying current I,with N turns and the radius of toroid R.
(5 marks)
00
9.b.
Show the inductance of the cable 
(5 marks)
00
10.a.
Derive the wave equation starting from the Maxwell's equations for free space.
(5 marks)
00
10.b.
In a material for which$\sigma$ =5.0 s/m and $\epsilon$=I ,the electric field intensity is E=250sin10¹⁰ t V/m. Find the conduction and displacement current densities and the frequency at which both have equal magnitudes.
(5 marks)
00
OR
11.a.
In free space 
V/m. Find the average power crossing a circular area of radius 2.5 cm in the plane z=0 . Assume Em=Hm $\eta$ and $\eta$g = 120π$\Omega$
(5 marks)
00
V/m. Find the average power crossing a circular area of radius 2.5 cm in the plane z=0 . Assume Em=Hm $\eta$ and $\eta$g = 120π$\Omega$
11.b.
Generate Ampere's law for time varying fields.
(5 marks)
00
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