Download Special Assignment_2_EEE

NIRMA UNIVERSITY
INSTITUTE OF TECHNOLOGY
B.Tech. Semester- I (ME, CL, EC, CH), July-Dec, 2014
EE101: ELEMENTS OF ELECTRICAL ENGINEERING
SPECIAL ASSIGNMENT – II
A: NUMERICALS
1
Three capacitors of 2μF, 3μF and 6μF are connected in series across a 500V dc supply. Determine (i)
the charge on each capacitor (ii) potential difference across each capacitor, and (iii) the energy stored
in each capacitor.
[Ans. (i) 500μC, (b) 250V, 166.67V, 83.3V, (iii) 0.0208J]
2
The capacitance of the capacitor formed by two parallel metal sheets, each 100cm2 in area, separated
by a dielectric 2mm thick is 2x10-10F. A potential difference of 20kV is applied across the capacitor.
Determine (i) total dielectric flux (ii) potential gradient, (iii) relative permittivity of the material and
(iv) electric flux density.
[Ans. (i) 4µC, (ii) 100kV/cm, (iii) 4.5, (iv) 400µC/m2]
3
A variable air capacitor has 15 movable plates and 16 fixed plates. The area of each plate is 15 cm2
and separation between opposite plates is 0.2 mm . Determine i) the maximum capacitance of this
variable capacitor; ii) the capacitance when 1/4th area of movable plates is overlapping the fixed
plates.
[Ans: i) 1.99nF ii) 0.498nF]
4A Capacitor of 80µF in series with a resistor of 1000Ω is suddenly connected across a 110V dc supply.
Calculate (I) time constant of the circuit, (ii) initial value of charging current, (iii) equation of
current, (iv) value of current after 0.08s, (v) rate at which current begins to decrease, (vi) voltage
across the capacitor after 0.04s, (vii) voltage across the resistor after 0.04s, and (viii) charging
current after 0.04s. [Ans. (i) 0.08s, (ii) 0.11A, (iii) 0.11e-12.5t, (iv) 0.0405A,(v) 1.375A/s, (vi) 43.28V,
(vii) 66.72V, (viii) 0.0667A]
5
A toroid is composed of three parts of different materials but of uniform cross sectional area. Their
mean length and relative permeability are 11=0.15m, µr1=1447 (cast steel), l2=0.30m, µr2=5969
(mild silicon steel, 13=0.45m, µr3=47750 (nickel iron). It is required to establish a flux of 0.6mWb
in the toroid. Calculate (i) magnetic field intensity in each part, (ii) mmf required and (iii) the
excitation current of the coil.
[Ans.: (i) 330AT/m, 80AT/m, 10AT/m, (ii) 78AT,
(iii) 0.78A]
3
2
cross
sectional
area
0.001m2
N
1
6
A series magnetic circuit comprises of three sections (i) length of 80mm with cross-sectional area
60mm2 (ii) length of 70mm with cross-sectional area 80mm2 and (iii) and air gap of length 0.5mm
with cross-sectional area of 60mm2. Sections (i) and (ii) are if a material having magnetic
characteristics given by the following table.
H (AT/m) 100 210 340 500 800
1500
B (Tesla) 0.2 0.4
0.6
0.8 1.0
1.2
Determine the current necessary in a coil of 4000turns wound on section (ii) to produce a flux
density of 0.7Tesla in the air-gap. Neglect magnetic leakage.
[Ans: 0.083A]
A cast steel magnetic structure made for a bar of section 8cm x 2cm is shown in figure. Determine
the current that the 500 turn – magnetizing coil on the left limb should carry so that a flux of 2mWb
is produced in the right limb. Take µr = 600 and neglect leakage.
[Ans: 3.02A]
7
25 cm
A
B
Φ
15 cm
C
Φ/2
Φ/
2
B: OBJECTIVES
If dielectric slab of thickness 5mm and relative permittivity 6 is inserted between the
plates of an air capacitor with plate separation of 8mm ,its capacitance is(a) decreased (b) almost doubled
(c) almost halved
(d) unaffected
Joule/coulomb is the unit of
(a) electric field potential
(b) potential
(c) charge
(d) none of the above
Three identical capacitors of capacitance C each, are connected in series and this
combination is connected in parallel with one more identical capacitor. The capacitance
of the whole combination will be
C
3
4C
3C
(a)
(b)
(c)
(d)
3
C
3
4
__________ is that property of a capacitor which delays any change of voltage across it.
(a) Inductance (b) Capacitance (c) Potential gradient (d) none of the above
The capacitance of a capacitor is not influenced by
(a) plate thickness (b) plate area
(c) plate separation
(d) nature of the material
In a capacitor, the electric charge is stored in
(a) metal plates (b) dielectric (c) both (a) and (b) (d) none of the above
Reciprocal of reluctance is
(a) reluctivity
(b) permeance
(c) permeability
(d) susceptibility
If the area of hysteresis loop of a material is large, the hysteresis loss in this material
will be
(a) zero
(b) small
(c) large
(d) none of the above
An air gap is usually inserted in magnetic circuits to
(a) increase mmf
(b) increase the flux (c) prevent saturation (d) none of the above
M.M.F. is analogus to
(a) Electric current in electric circuit (b) Current density in the conductor
(c) Electromotive force
(d) Voltage
1.
2.
3.
4.
5.
6.
7
8
9
10
1.
2.
3.
4.
5.
C: SHORT QUESTIONS
Discuss the different types of magnetic materials.
Enumerate the importance of magnetic circuit.
Discuss the behavior of capacitor with DC supply.
What are the uses of multi plate capacitors ?
Elaborate the different types of capacitors.