1) A capacitor is used to store electric charges by doing work to deposit the charges, and this work done is stored as electric potential energy. 2) The potential energy stored in a capacitor is calculated as one-half of the capacitance C multiplied by the voltage V squared. 3) When a dielectric material is placed in a capacitor, the charges in the dielectric polarize and slightly displace, which decreases the voltage across the capacitor but increases its capacitance.

1. ENERGY STORED IN A CAPACITOR

2. • Capacitor is a device which is used to store charges
• To deposit charges we have to do some work
• We know that whenever we do work in a electric field it store in the
form of potential energy
• W=P.E
• So if some how we calculate work done we can calculate P.E stored
inside the capacitor
ENERGY STORED IN A CAPACITOR

3. • Derivation for P.E
• As we know that, V =
W
q
• W = V q0
• Before charging the electric potential difference between plates is ZERO and
it finally become V when charge q is deposited on it
• Average V =
0+𝑉
2
• Average V =
1
2
𝑉
• W =
1
2
𝑉q
• P.E =
1
2
𝑉q
ENERGY STORED IN A CAPACITOR

4. • P.E =
1
2
𝑉(CV)
• P.E =
1
2
CV2
• Energy stored in term of electric field
C=
𝑨𝛜 𝟎 𝛜 𝒓
𝒅 V = Ed
P.E =
𝟏
𝟐
(
𝑨𝛜 𝟎 𝛜 𝒓
𝒅
)(Ed)2
P.E =
𝟏
𝟐
𝛜 𝟎 𝛜 𝐫 E2(Ad)
ENERGY STORED IN A CAPACITOR

5. • Energy density
• Energy density =
𝑒𝑛𝑒𝑟𝑔𝑦
𝑣𝑜𝑙𝑢𝑚𝑒
• Energy density =
𝟏
𝟐
𝛜 𝟎 𝛜 𝐫 E2(Ad)
𝐴𝑑
• Energy density =
𝟏
𝟐
𝛜 𝟎 𝛜 𝐫 E2
Mass density =
𝒎𝒂𝒔𝒔
𝒗𝒐𝒍𝒖𝒎𝒆
ENERGY STORED IN A CAPACITOR

6. • Definition
• When a electric material is placed in an electric field the negative and positive
charges of dielectric are slightly displaced. This phenomenon is called
polarization and dielectric is said to be polarized
• Effect
• Voltage decreases and capacitance increases
• Explanation
C =
𝑸
𝑽
ELECTRIC POLARIZATION OF
DIELECTRIC

7. CHARGING AND DISCHARGING
OF CAPACITOR

8. • Definition
• The time during which the capacitor charges to 63% of its maximum value is
called time constant
• formula
• Time constant = RC
If RC is lower the charging
and discharging is rapid
If RC if greater then charging and
discharging is higher
CHARGING AND DISCHARGING
OF CAPACITOR

9. Charging of capacitor
CHARGING AND DISCHARGING
OF CAPACITOR

11. ANSWER: A
PRACTICE TEST

12. PRACTICE TEST
ANSWER: D

13. PRACTICE TEST
ANSWER: A