Capacitor,,,types,,,construction,,,,insulating material

2. PRESENTATION
Presented To:
Sir Shahid
Iqbal Presented by:
Muhammad Usman
University of Gujrat
Hafiz Hayat
Batch-2015

3. Basic
Electronic
Capacit
or

4. The Device Which Is Used To Store Charge
Is Called Capacitor.

7. TYPES OF CAPACITORS
Parallel-Plate Capacitor Cylindrical Capacitor
A simple capacitor consists of two parallel conducting plates
separated by air or some dielectric(insulating material).
A cylindrical capacitor is a parallel-plate capacitor that has
been rolled up with an insulating layer between the plates.

8. Parallel Plate Capacitor:-
Consists of two parallel
conducting plates separated by air, or some
insulating material called dielectric.
+
Q
-
Q
+
Q
-
Q

9. • A simple parallel-plate capacitor consists of two
conducting plates of area A separated by a
distance d.
• Charge +Q is placed on one plate and –Q on
the other plate.
• An electric field E is created between the
plates.

10. d
A
C 

11. Charging Of a
Capacitor
The plates are connected to a battery of
voltage v, then one of the plate has charge
+q and other have –q. These charges remain
on inner surface of the plates due to
attraction between the opposite charges.
Q ∝ V
Q = CV
C=Q/V
There is constant of proportionality called the
capacitance of capacitor

12. Charging and Discharging of a Capacitor
The circuit consisting of a capacitor and resistor is called R-C circuit.

13. Dependence of Capacitance:
Capacitance depends on
following factors.
Geometry of the capacitor i.e. area of the plates and
separation between the plates.
Medium between the plates.
Capacitance of Parallel Plate Capacitor:
Consider a parallel plate capacitor as shown in figure. Let A is the area of each plate, d is
distance between the plates, Q is the charge stored in each plate, V is the potential
difference between the plates, E is the electric field between the plates and σ is the surface
charge density of plates.
Capacitance When Air or Vacuum Between the
Plates:
Let there is air or vacuum between the plates of the capacitor. Then,
𝑪 𝑽𝒂𝒄=
𝑸
𝑽
……….(1)
We know that,

14. Or
V=Ed…… eq. (2)
As electric intensity between two oppositely charged plates is given by
E=
𝝈
𝜺°
……… eq.(3)
Putting values in equation (2) we get,
V=
𝝈𝒅
𝜺°
………. eq.(4)
Surface density of charge on the plates is given by,
𝛔 =
𝐐
𝐀
…… eq.(5)
Using equations (4) and (5) in equation (1),we get
𝐂 𝐯𝐚𝐜=
𝝈𝑨
(
𝝈𝒅
𝜺°
)
OR
𝐂 𝐯𝐚𝐜=
A 𝜺°
𝒅
……. Eq.(6)
ii) With dielectric as the medium:
if an insulating material ,called dielectric ,

15. Permitivity 𝛆 𝐫 is placed between the two plates, then the capacitance of capacitor increased by the
factor 𝛆 𝐫 called as dielectric constant, eq.(6) can be written as
𝑪 𝒎𝒆𝒅=
A 𝛆 𝐫 𝜺°
𝒅
………. Eq.(7)
Energy Stored in a Capacitor
Capacitor is a device used to store the charge. In other
words, it is a device for storing electric P.E. because work is to be done to deposit charge
on the plates. It increases the potential difference between plates and a large amount of
work is needed to bring up next increment of charge. Initially when the capacitor is
uncharged, the potential difference between plates is zero and finally it becomes V when
charge q Is deposited on each plate.
Average potential difference is =
0+𝑉
2
=
1
2
V
Work = Average potential difference x Charge
W= (1
2
V)(q)
P.E. =
1
2
qV
P.E.=
𝟏
𝟐
(CV)(V) [∴ q=CV]
Energy=
𝟏
𝟐
C𝑽 𝟐
………. (1)

16. Energy Stored in Terms of Electric Field
When we consider that energy is
being stored between the two plates rather than the potential energy of charges on the
plates then we put
C=
A 𝛆 𝐫 𝜺°
𝒅
It is the capacitance of parallel plate capacitor with a dielectric medium
Putting these values in equation(1), we get
Energy=
𝟏
𝟐
(
A 𝛆 𝐫 𝜺°
𝒅
) (ED) 𝟐
Energy=
𝟏
𝟐
𝜺° 𝛆 𝐫 𝑬 𝟐(𝐀𝐝)
It is an expression for energy stored in the electric field between the plates.
Energy Density
Energy density is defined as the energy stored per unit volume.
Energy density=
𝐞𝐧𝐞𝐫𝐠𝐲
𝐯𝐨𝐥𝐮𝐦
Volume between the plates=Ad
Energy density=
𝟏/𝟐[𝜺° 𝛆 𝐫 𝑬 𝟐](𝐀𝐝)
𝑨𝒅
Energy density=
𝟏
𝟐
𝜺° 𝛆 𝐫 𝑬 𝟐

19. • 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.
For a changing current, the drop in charge, DQ is given by:
DQ = -IDt (minus because charge Large at t = 0 and falls as
t increases)
So DQ = -QDt/RC (because I = Q/RC)
Or -DQ/Q = Dt/RC

27. This is End to my
presentation.
Thanks to all of you.
Any Question?