The document discusses the effect of dielectrics on capacitor capacitance, explaining that inserting a dielectric increases energy storage capacity, characterized by the dielectric constant k. It also describes how a metallic slab affects capacitance by creating two capacitors in series with an induced charge on the slab, resulting in a net zero charge within the slab. Additionally, the impact of two different dielectric slabs filling a capacitor's space is analyzed, treating them as capacitors in parallel.

1. Effect of dielectricsonEffect of dielectricson
CapacitanceCapacitance

2. Dielectric
• A dielectric is a nonconducting material
inserted between the plates of a
capacitor.
• A dielectric increases the ability of a
capacitor to store energy.
• If the dielectric completely fills the space
between the plates, the capacitance
increases by a factor k, called the
dielectric constant.
d
Aεk
C o ⋅⋅
=

3. Dielectric
•When a dielectric is
inserted between the
plates of a charged
capacitor that is not
connected to a battery
(a source of additional
charge), but the
voltage is reduced by
a factor k.
new
old
V
V
k =

4. Dielectrics

5. Effect of the Dielectric Constant
o
dielectric
E
E
k
= o
dielectric
E
E d d
k
• = •
r
r rr
l l
o
dielectric
V
V
k
=
Potential difference with a dielectric
is less than the potential difference
across free space
o
o
Q Q
C k k C
V V
= = × = × Results in a higher capacitance.
Allows more charge to be stored before breakdown
voltage.

6. Effect of a Metallic Slab Between the Plates
A parallel-plate capacitor has a plate separation d
and plate area A. An uncharged metallic slab of
thickness a is inserted midway between the plates.

7. Charge on one plate must induce a charge of equal magnitude but
opposite sign on the near side of the metallic slab.
Net charge on the slab is zero, electric field inside the slab is zero.
Capacitor = two capacitor in series, each having a plate separation
of (d-a)/2 as shown.

8. ( ) ( )
( )
1 2
1 1 1 1 1 1
;
2 2
1 2 1 2 1 1
; ;
2
2
1
;
o oT T
o o oT T T
o
T
T o
A AC C C C
d a d a
A A AC C C
d a d a d a
Ad a
C
C A d a
ε ε
ε ε ε
ε
ε
= + = +
× ×
− −
= = =
× × × ×
− − −
×−
= =
× −

9. Effect of a Metallic Slab between the plates
What are the differences in the result as compared to the previous
example if we insert the metallic slab as shown?

10. Two Dielectric Slabs
• Consider a parallel-plate
capacitor that has the space
between the plates filled
with two dielectric slabs,
one with constant k1 and
one with constant k2.
• The thickness of each slab
is the same as the plate
separation d and each slab
fills half the volume between
the plates.
• The two different dielectric
slabs represent two
capacitors in parallel with a

11. Two Dielectric Slabs
1 2
21
1 2
1 2
2 2
2
( )
2
T
oo
T
o o
T
o
T
C C C
k Ak A
C
d d
k A k A
C
d
A k k
C
d
εε
ε ε
ε
= +
× ×× ×
= +
× ×
× × + × ×
=
×
× × +
=
×

12. Hey Friend,
This was just a summary on Effect of Dielectric on
Capacitance. For more detailed information on this topic,
please type the link given below or copy it from the
description of this PPT and open it in a new browser window.
www.askiitians.com/iit-jee-electrostatics/effect-of-
dielectric-on-capacitance/