CHAPTER 2.2 CAPACITOR, CAPACITANCE, CAPACITANCE REACTANCE, ENERGY IN CAPACITOR.

BJI 10013
ELECTRICAL AND

ELECTRONICS
SYSTEM

CHAPTER 2.2

CAPACITOR,
CAPACITANCE,
CAPACITANCE REACTANCE,
ENERGY IN CAPACITOR.

BAHARUDDIN BIN MOHD ZANGGI
Pensyarah JKM, PSAS

SYLLABUS

2.2 Explain the basic principle of capacitors

2.2.1 Define capacitors and identify its unit
2.2.2 Describe and draw a diagram to show existence of

charge on capacitor plates.
2.2.3 Explain capacitors in series and parallel circuits to find

total capacitance.
2.2.4 Explain the effects of capacitors in electrical circuits
2.2.5 Determine capacitance and energy stored by a

capacitor.

International System of Unit

Basic SI Unit : Basic Unit Symbol
Meter m
Quantity Kilogram kg
Length
Mass Second S
Ampere A
Time
Electric Current Kelvin K
candela cd
Thermodynamic Temperature

Luminous Intensity

The SI prefixes

multiplier prefix symbol multiplier prefix symbol
1018 exa E 10-1 deci d
1015 peta P 10-2 centi c
1012 tera T 10-3 milli m
109 giga G 10-6 micro µ
106 mega M 10-9 nano n
103 kilo k 10-12 pico p
102 hecto h 10-15 femto f
10 deka da 10-18 atto a

CAPACITOR

CAPACITOR

• Capacitor is an electrical device with ability of
dielectric to hold or store electric charge in its
electric field.

• It is a passive element in a linear circuit.
• Unit is Farad (F) and symbol is C.

CAPACITOR

• The quantity and duration of energy can be saved
depends on the capacitance of the capacitor.

• Electrical energy stored in the capacitor is in a
form of charge.

• A plate will has a negative charge (-ve) and the
other plate is positive charge (+ve).

VIDEO OF CAPACITOR

1. CHARGING AND DISCHARGING CAPACITOR
2. https://www.youtube.com/watch?v=X4EUwTwZ110

CAPACITOR

• Capacitor or condenser built with two-conductor
or plate arranged opposite each other.

• It separated by insulating material called the
dielectric.

CAPACITOR

TYPES OF CAPACITOR

• Dielectric Air Convertible Capacitor, Paper
Capacitor, Polyester Capacitor, Mica Capacitor,
Ceramic Capacitor, Electrolytic Capacitor and
Tantalum Capacitor

TYPES OF CAPACITOR

VIDEO OF CAPACITOR

2. CAPACITOR POLARITY (REPLACEMENT TUTORIAL)

CAPACITANCE

• Capacitance is a characteristic of a capacitor to
store electrical energy.

• It is define as the quantity or amount of electric
charge needed to make a difference between the
two plates.

CAPACITANCE

• Capacitance of 1 Farad means a capacitor can
store 1 coulomb of electrical charge when voltage
is applied to the capacitor is 1 volt.

• The more charged stored for a given voltage, the
higher capacitance

• A larger capacitance can store more charge

CAPACITANCE

• A larger capacitance can store more charge.
• The amount of charge (q) stored is directly

proportional to the applied voltage (V).

CAPACITANCE

CAPACITANCE

• Typically the unit use for capacitor are
microFarad (μF) or pikoFarad (pF).

EXAMPLE 2.2.1

How much charge is stored if a 2µF
capacitor is connected across a 60V
supply.

• Ans : 0.12 mC

EXAMPLE 2.2.2

• A constant current of 10 mA charges a 30µF
capacitor for 1 s. How much is the voltage across
the capacitor?

Hint : Q = It
Q = CV

ENERGY STORED IN CAPACITOR

• The electrostatic field of the charge stored in a
dielectric has electric energy supplied by the
voltage source that charges C.

• Energy can calculated:

• Q (charged stored in the dielectric) (Coulombs @C)
• V (Voltage across the capacitor)
• E (Electric energy in Joules)

ENERGY STORED IN CAPACITOR

• Since Q = CV. This formula can be derived as:

EXAMPLE 2.2.3

A capacitor of 10pF with 15V supply across it.
Calculate :

a ) Charge stored in the capacitor
b) Energy stored in the capacitor

Exercise 1

• Capacitor with 8pF connected to the 600V power
supply. Calculate the charge and energy that can
be stored by the capacitor.

TYPES OF CAPACITORS

• Different types of capacitors are manufactured
for specific values of C. The value based
according to the dielectric.

• Common types are:

i. Mica
ii. Ceramic
iii. Paper
iv. Film
v. Electrolytic

TYPES OF CAPACITORS

MICA

• Small with high working voltage
• The working voltage is the voltage limit that

cannot be exceeded.

TYPES OF CAPACITORS

CERAMIC
• Small non-polarized capacitor made of sand earth

fired under extreme heat.
• In a form of disk capacitors
• 1 pF or less up to 1µF

TYPES OF CAPACITORS

PAPER
• Often used for medium capacitance value of 0.001

– 1µF
• No required polarity
• Two types; foil type and metallized type.
• Used in radio and timer circuit

TYPES OF CAPACITORS

FILM
• Small and non polarized
• High capacitance due to larger plate area

TYPES OF CAPACITORS

ELECTROLYTIC
• High capacitance but not precise and tend to have

more leakage current.
• Polarized

CAPACITOR APPLICATIONS

1. Increasing the circuit power factor.
2. Reducing the fireworks/spark during the switch is

on inside the circuit.
3. Reduce radio interference test in the starter circuit

pendaflour light.
4. Strengthen the electric current.
5. Store electrical charges.
6. Used in AC to DC converter circuit
7. In electric AC motor to make high initial torque.

FACTORS THAT INFLUENCE CAPACITANCE

Three factors that influence the capacitance

1. Plat area, A
2. Thinner Dielectric, d
3. Dielectric constant, KE

FACTORS THAT INFLUENCE CAPACITANCE

Plat area, A C ∝ A

• Larger plat area increase capacitance.
• Capacitance is directly proportional to the plat area.
• Larger plate area means more dielectric surface can

contact each plate.
• So that the field can store more charge in the

dielectric.
• The larger plate area, the more charge is stored for the

same applied voltage

FACTORS THAT INFLUENCE CAPACITANCE

Thinner Dielectric, d

• Capacitance is inversely proportional to the
distance between the plates.

• Capacitance of a capacitor change when the
distance between the plates changes.

• Capacitance will increase when the plates when
the plate is brought closer.

FACTORS THAT INFLUENCE CAPACITANCE

Dielectric constant, KE

• Indicates the ability of an insulator to concentrate
electric flux.

• Capacitance is directly proportional to the
dielectric constant KE

C ∝ KE

FACTORS THAT INFLUENCE CAPACITANCE

Dielectric constant, KE

FACTORS THAT INFLUENCE CAPACITANCE

FORMULA

EXAMPLE 2.2.5

• Calculate C for two plates, each with an area 2 m2
separated by 1 cm with a dielectric of air

CAPACITOR CIRCUIT ANALYSIS

The method of the capacitor circuit analysis is
different with the method of circuit analysis for
resistor and inductor.

• There are 3 types of circuit analysis in capacitor:

1. Series
2. Parallel
3. Combination of series and parallel

SERIES CAPACITOR

• When capacitors are connected in series, the total
capacitance (CT)is less than any one of the series
capacitors' individual capacitances.

• If two or more capacitors are connected in series, the
overall effect is that of a single (equivalent) capacitor
having the sum total of the plate spacings of the
individual capacitors.

SERIES CAPACITOR

SERIES CAPACITOR

EXAMPLE 2.2.6

Ans ;
a) 8.571 x 10-6 F
b) 1.714 mC
c) 28.567 V, 171.40 V



PARALLEL CAPACITOR

• The total capacitance of capacitors in parallel is
equal to the sum of their individual capacitances.

PARALLEL CAPACITOR

EXAMPLE 2.2.7

Calculate the total capacitance of the three (3)
capacitor where the value of each capacitance is
120μF when it is connected in:
a. Parallel
b. Series

Ans : 360µF, 40µF



EXAMPLE 2.2.8

Two capacitors each value is 6μF and 10μF is
connected in series with a 200V power supply.
Calculate;

a. Total capacitance
b. Charge in each capacitor
c. Voltage across each capacitor.

Ans :
a) 3.75 µF
b) 750µC
c) V1 = 125V, V2 =75 V