1) A capacitor is a device that stores electric charge. A simple capacitor consists of two parallel conducting plates separated by an insulating medium called a dielectric. 2) When a voltage is applied across the plates, positive and negative charges accumulate on the inner surfaces of each plate. The amount of charge stored is directly proportional to the voltage. 3) The capacitance of a capacitor is a measure of how much charge it can store. It is calculated as the ratio of stored charge to voltage. The capacitance increases if the plate area or dielectric constant increases, or if the distance between plates decreases.

1. CAPACITOR
Dr. Nadeem Khalid
AL-AQSA ACADEMY, LAHORE

2. • Definition
• The device which is used to store electric charge is called capacitor
CAPACITOR

4. • A simple capacitor consist of two parallel conducting plates separated
by air, or some insulating medium is called parallel plate capacitor
• The insulating medium is known as dielectric
PARALLEL PLATE CAPACITOR

5. • If the plates are connected to a battery of voltage V the one of the
plate has + Q charge and the other plate have – Q charge. These
charges remain on the inner surface of the plates due to attraction
between the opposite charges
• It is observed that if the amount of charge stored increased the
potential difference between plates also increase
• Q∝ 𝑉
• Q = CV
• C =
𝑄
𝑉
• Here C is the constant of proportionality called capacitance of capacitor
CHARGING OF CAPACITOR

6. • Definition
• The capacity of a capacitor to store charges is known as Capacitance
• Formula
• C =
𝑄
𝑉
• Dependence
• Area of plate
• Distance between plates
• Medium present between plates
• Units
• Farad(F)
• Farad
• if one coulomb charge store on capacitor plates produce a potential difference of
one volt then capacitance of this capacitor will be one farad
• 1 farad =
1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏
1 𝑣𝑜𝑙𝑡
CAPACITANCE

7. • Consider a parallel plate capacitor. Let
• A = area of each plate
• d = distance between the plates
• Q = charge store on each plate
• V = potential difference between plates
• E = electric field
• 𝜎 = surface charge density
CAPACITANCE OF A PARALEL PLATE
CAPACITOR

8. • Capacitance when air or vacuum between plates
• Cvac =
𝑄
𝑉
…….(1)
• Cvac =
𝜎𝐴
𝜎𝑑
ϵ0
• Cvac =
𝐴ϵ0
d
CAPACITANCE OF A PARALEL PLATE
CAPACITOR
E=
𝑽
𝒅
V = Ed
E =
𝝈
𝛜 𝟎
V = =
𝝈𝒅
𝛜 𝟎
𝝈=
𝑸
𝑨
Q = 𝝈𝑨

9. • Capacitance with dielectric as medium
• If an insulating material of relative permittivity ϵr is placed between plates the
capacitance of capacitor is increased by the factor ϵr called as dielectric
constant
• Cmed =
𝐴ϵ0 ϵr
d
CAPACITANCE OF A PARALEL PLATE
CAPACITOR

10. • How capacitance increase
• C =
𝑄
𝑉
• by placing dielectric voltage decrease so capacitance increase
• Dielectric constant
• Ratio of capacitance of a parallel plate capacitor with a dielecric to its
capacitance with vacuum or air as a medium
• ϵr =
Cmed
Cvac
CAPACITANCE OF A PARALEL PLATE
CAPACITOR

12. PRACTICE TEST
Answer: A
C =
𝑄
𝑉

13. PRACTICE TEST
Answer: A
Cmed =
𝐴ϵ0 ϵr
d

14. PRACTICE TEST
Answer: C
Cvac =
𝑨𝛜 𝟎
𝒅