Jawaharlal Nehru Technological University Kakinada 2008 B.Tech Electrical and Electronics Engineering ELECTROMAGNETIC FIELDS - Question Paper

(b) A magnetic circuit comprising a toroid of 500 turns and an area of 6cm2
and
mean radius of 15cm and carries a current of 4A. obtain reluctance and ?ux
presume r=1. [8+8]
8. (a) discuss the Maxwell’s equations for harmonically time varying ?elds.
1 of 2Code No: 07A3EC04 Set No. 2
(b) A faraday’s copper disc 0.3m diameter is rotated at 60 rps on a horizontal axis
perpendicular to and through the centre of disc, the axis laying in a horizontal
?eld of 20Tesla. Determine emf measured ranging from the brushes. [8+8]
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2 of 2Code No: 07A3EC04 Set No. 3
II B.Tech I Semester Regular Examinations, November 2008
ELECTROMAGNETIC FIELDS
( Common to Electrical & Electronic Engineering and Electronics & Control
Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
? ? ? ? ?
1. (a) State and discuss Coulomb‘s legal regulations of electrostatic ?eld in vector form.
(b) It is needed to hold 4 equal point charges to every in equilibrium at the
corners of a square. obtain the point charge, which will do this if placed at the
center of the square. [8+8]
2. (a) For a pure dipole paz C- m at the origin in free space, ?nd the potential at a
point A (r, ?, f = p
2 )
(b) What is the electric ?eld at (x=0, y=0, z=5m) due to a pure dipole 1az c-m
at the origin? [8+8]
3. (a) State and prove the conditions at the boundary ranging from 2 dielectrics.
(b) Determine the resistance of insulation in length ‘L’ of co-axial cable as inner
and outer radii are ‘a’ and ‘b’ respectively. [8+8]
4. A conductor is in the form of a Regular polygon of n sides inscribed in a circle of
radius R. Show that the expression for B at the center for a current is provided by
|B| =

n0
I/ 2pR

Tan
p/n. [16]
5. (a) define the application of Amperes circuital legal regulations to an unsymmetrical ?eld.
(b) In the cylindrical region 0 < r < 0.8m, J = 3e-5r
az A/m2
. Determine H =
Hfaf every where. [16]
6. obtain the torque which will be produced on a rectangular current loop if placed to
a magnetic ?eld B show that T = m × B also holds for the system. [16]
7. obtain the mutual inductance ranging from 2 toroidal windings which are closely wound
on iron core of relative permeability 900. The mean radius of the core is 5cm and
radius of its cross-section is 5cm. every winding has also 800 turns. [16]
8. (a) discuss Faraday’s legal regulations of electromagnetic induction and derive the expression
for induced emf.
(b) obtain the conduction and displacement current densities in a material having
conductivity of 10-3
S/m and er= 2.5, if the electric ?eld in material is, E =
5.8×10-6
sin (9×109
t) V/m. [8+8]
? ? ? ? ?









1 of 1Code No: 07A3EC04 Set No. 4
II B.Tech I Semester Regular Examinations, November 2008
ELECTROMAGNETIC FIELDS
( Common to Electrical & Electronic Engineering and Electronics & Control
Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
? ? ? ? ?
1. (a) discuss coulomb‘s legal regulations.
(b) 2 small identical conducting spheres have charge of 2nC and - 0.5nC re-
spectively. when they are placed four cm apart what is the force ranging from them.
If they are brought into contact and then separated by four cms what is the force
ranging from them. [6+10]
2. Show that the torque acting on an dipole of movement p due to an electric ?eld E
is p×E calculate the torque for a dipole consisting of one c charges in an electric
?eld E = 103
(zax - ay - az) separated by one mm and located on the z-axis at the
origin. [16]
3. (a) compute the capacitance of a parallel plate capacitor with subsequent details.
Plate area = 150 sq.cm.
Dielectric er1 = 3, d12 = 4mm
Dielectric er2 = 5, d12 = six mm
If 200 V is applied across the plates what will be the voltage gradient across
every dielectric.
(b) The permittivity of the dielectric of parallel plate capacitor increases uniformly
from 1 plate to the other. If A is the surface areas of the plate and d is the
thickness of dielectric, derive an expression for capacitance. [8+8]
4. 2 narrow circular coils A and B have a common axis and are placed 10 cms
apart. Coil A has 10 turns of radius 5cm with a current of 1A passing through it.
Coil B has a single turn radius 7.5 cms. If the magnetic ?eld at the centre of coil
A is to be zero, what current should be passed through coil B. [16]
5. (a) De?ne and establish Amperes circuital legal regulations for electromagnetic ?eld.
(b) An H due to current source is provided by H = (y cos ax) ax + (y.ex) az. define
the current density over the yz- plane. [16]
6. Justify the formula T = m × B for a circular coil carrying a steady current I is
placed such that its plane lie in the x-y plane and also parallel to the direction of
a uniform magnetic ?eld B. [16]
7. (a) discuss the di?erence ranging from magnetic vector potential and magnetic scalar
potential
1 of 2Code No: 07A3EC04 Set No. 4
(b) Current in a coil is increased from 0 to 10 Amps at a uniform rate is five sec.
It is obtained that this coil develops self induced emf of 100V where as an emf
of 20V is decreased in a neighbouring coil. calculate self inductance of the ?rst
coil and mutual inductance ranging from the 2 coils. [8+8]
8. (a) Derive the expression for 1 of the Maxwell’s formula ? × E = -?B
?t
(b) obtain the frequency at which conduction current density and displacement
current density are equal in a medium with s= two × 10-4
mho/m and er=81.
[8+8]
? ? ? ? ?
2 of 2

Earning:   Approval pending.