Here i uploaded ppt of BTECH SEM II (EEE)

1. Unit 3
ELECTROSTATICS MAGNETISM AND
ELECTROMAGNETISM
Course : B.Tech
Branch : EE
Semester : II
Subject : Elements of Electrical Engineering

2. Definitions of Electrostatic
Electrostatics is a branch of physics that deals with the
phenomena and properties of stationary or slow-moving electric
charges with no acceleration.
Capacitors
A capacitor is a device that stores electric
charge. capacitor consists of two conductors separated by
an insulator.
• Capacitors have many applications:
– Computer RAM memory and keyboards.
– Electronic flashes for cameras.
– Electric power surge protectors.
– Radios and electronic circuits.

3. What is a capacitor?
• Electronic component
• Two conducting surfaces separated by an insulating material
• Stores charge
• Uses
– Time delays
– Filters
– Tuned circuits

4. Capacitor construction
• Two metal plates
• Separated by insulating
material
• ‘Sandwich’ construction
• ‘Swiss roll’ structure
• Capacitance set by...
d
A
C 
FIG 2

5. Defining capacitance
• ‘Good’ capacitors store a lot of charge…
• …when only a small voltage is applied
• Capacitance is charge stored per volt
• Capacitance is measured in farads F
– Big unit so nF, mF and F are used
V
Q
C 

6. • At some time t, with charge Q on the
capacitor, the current that flows in an interval
Dt is:
I = DQ/Dt
• And I = V/R
• But since V=Q/C, we can say that
I = Q/RC
• So the discharge current is proportional to the
charge still on the plates.

7. • For a changing current, the drop in charge, DQ
is given by:
DQ = -IDt (minus because charge Iarge at
t = 0 and falls as t increases)
• So DQ = -QDt/RC (because I = Q/RC)
• Or -DQ/Q = Dt/RC

8. Capacitors in Parallel
VC
VCCC
VCVCVC
QQQQ
eq



)( 321
321
321
...321  CCCCeq
Capacitors in Parallel:
Fig 3

9. Force on current carrying conductor in magnetic
field
Fig 4

10. the figure, a conductor lying vertically in a uniform
horizontal magnetic field of strength H. If l is the length
of the conductor tying within this magnetic field and i is
the current through it, then the force experienced by
the conductor will be
F = B.i.l Newton
= μ0.μr.H.i.l Newton
The direction of the force F can also be
determined by Flemming's Left Hand Rule. As per this
rule, if any one holds out his or her hand with fore
finger, second finger and thumb at right angle to each
other, then his or her fore-finger will indicate the
direction of magnetic field, the second finger will
indicate the direction of flow of current and the thumb
will give the direction of force or motion of the
conductor.In this case the force experienced by the
conductor will be
F = B.i.l.sin(θ) Newton.

11. Comparison between Electric and
Magnetic Circuits
fig

12. Magnetic Equivalent Circuit
Fig 6

13. Parallel Magnetic Circuit
l2l1
l3
I
N
S1
S2S3
+
- NI
1
3
2
I
II
Loop I
NI = S33 + S11
= H3l3 + H1l1
Loop II
NI = S33 + S22
= H3l3 + H2l2
Loop III
0 = S11 + S22
= H1l1 + H2l2
From self making from EEE (U.A.Patel)

14. Magnetic Circuit with Air Gap
lc
i
N lg
+
F
-

c
g
g
g
g
c
c
c
ggcc
gC
g0
g
g
cc
c
c
A
B
A
B
densityFlux
lHlHNi
Ni
A
l
A
l











;
;
From self making from EEE (U.A.Patel)

15. Series circuits
A series circuit has only one
current path
Current through each component is the
same
In a series circuit, all elements
must function for the circuit
to be complete
Fig 7

16. Parallel circuits
A parallel circuit has more than one
current path branching from the energy
source Voltage across each pathway is the
same. In a parallel circuit, separate current
paths function independently of one
another. For parallel voltage sources, the
voltage is the same across all batteries, but
the current supplied by each element is a
fraction of the total current

17. Lenz’s Law
• Faraday’s law gives the direction of the induced emf and
therefore the direction of any induced current. Lenz’s law is
a simple way to get the directions straight, with less effort.
• Lenz’s Law:
The induced emf is directed so that any induced current
flow will oppose the change in magnetic flux (which
causes the induced emf).
This is easier to use than to say ...
Decreasing magnetic flux  emf creates additional
magnetic field
Increasing flux  emf creates opposed magnetic field

18. Fleming's Right-Hand Rule
• The Thumb represents the
direction of Motion of the
conductor.
• The First finger represents
the direction of the Field.
(north to south)
• The Second finger
represents the direction of
the induced or
generated Current (the
direction of the induced
current will be the direction
of conventional current;
from positive to negative).
Fig 8

19. Fleming's Left-Hand Rule
• A left hand can be held, as
shown in the illustration,
so as to represent three
mutually orthogonal axes
on the thumb, first finger
and middle finger.
• Each finger is then
assigned to a quantity
(mechanical force,
magnetic field and electric
current). The right and left
hand are used for
generators and motors
respectively.
Fig 9

20. Induced emf
• Dynamically Induced emf
• Statically Induced emf
Dynamically Induced emf
By moving the conductor keeping the
magnetic field system stationary, thus emf
induced in the conductor is called Dynamically
Induced emf

21. Statically Induced emf
• The emf induced by variation of flux is termed
as Statically Induced emf
• In this case conductor is held stationary and
magnetic field varies.
• Two Types :
1) Self Induced emf
2) Mutually Induced emf

22. 1) Self Induced emf
Fig 9

23. 2) Mutually Induced emf
Fig 10

24. REFRENCES : IMAGES
• http://upload.wikimedia.org/wikipedia/commons/thumb/3
/35/Parallel_plate_capacitor.svg/250px-
Parallel_plate_capacitor.svg.png
• http://www.physicstutorials.org/images/stories/electrostat
ics/capacitorinparallel.png
• http://www.physicstutorials.org/images/stories/electrostat
ics/capacitorinseries.png
• http://www.electrical-engineering-assignment.com/wp-
content/uploads/2013/05/114-220x300.png
• http://www.scielo.br/img/revistas/jbsmse/v29n1/a13fig03.
gif

25. • http://upload.wikimedia.org/wikipedia/commons/thumb/0
/0d/Series_circuit.svg/189px-Series_circuit.svg.png
• http://www.electrical4u.com/forum/fleming-left-hand-
rule.png
• http://electrical4u.com/electrical/wp-
content/uploads/2013/05/fleming-right-hand-rule.jpg
• http://www.electrical-engineering-assignment.com/wp-
content/uploads/2013/05/173.png
• http://www.electrical-engineering-assignment.com/wp-
content/uploads/2013/05/251.png

26. REFERENCE- BOOK
• B.L.Theraja, “Electrical Technology Vol.1”, S.Chand Publication.
• D.P.Kothari, “Basic Electrical Engineering”, Tata McGraw-Hill
publication.
• U.A.Patel “Circuits and Networks”.
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