Capacitors store electrical energy and oppose sudden changes in voltage. They consist of two conducting plates separated by an insulator. Capacitance depends on the plate area, separation distance, and the dielectric material. Common types include paper, mica, ceramic, electrolytic and polymer capacitors. Capacitors are used for blocking DC, coupling stages, filtering, and charge storage. Their specifications include capacitance value, voltage rating, tolerance, and temperature coefficient. Variable capacitors allow tuning of capacitance through mechanical adjustment of plate overlap area.

1. CAPACITORS
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2. Capacitors
A capacitor is a passive component which has the ability to store
energy in the form of electrical charge, producing a potential
difference across its plates and release them whenever desired.
Property of a capacitor to store charge on its plates in the form of an
electrostatic field is called the Capacitance of the capacitor.
It can also be defined as the property of a circuit to oppose sudden
change in voltage in the circuit.
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3. A capacitor consists of two conducting plates, separated either by air or by an
insulating material known as dielectric.
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4. Capacitance, 𝐶 =
𝜀𝐴
𝑑
=
𝜀0𝜀𝑟𝐴
𝑑
where
A is the area of plates, d is the plates separation,
ε is the absolute permittivity of the dielectric medium
ε0 is the permittivity of free space ( 8.84 x 10-12 F/m )
εr is the relative permittivity of the material being used as the dielectric
Unit of capacitance is Farad (abbreviated as F), named after the British physicist
Michael Faraday.
Commercially available capacitors are much smaller in value (µF or pF)
1µF = 10−6F
1pF = 10−12F
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5. Action of a capacitor
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6. The amount of charge stored in a capacitor is proportional to applied voltage and
the proportionality constant is capacitance
Q = CV
where
Q - Charge stored in Coulombs
C - Capacitance in farad
V - Voltage across the capacitor in Volts
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7. • Current through a capacitor, 𝑖 =
𝑑𝑄
𝑑𝑡
𝑖 =
𝑑(𝐶𝑉)
𝑑𝑡
= 𝐶
𝑑𝑉
𝑑𝑡
Consider the circuit
𝑣 = 𝑣0𝑆𝑖𝑛𝜔𝑡
C
i
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8. 𝑖 = 𝐶
𝑑(𝑣0𝑆𝑖𝑛𝜔𝑡)
𝑑𝑡
= 𝐶𝑣0 cos 𝜔𝑡 𝜔
= 𝐶𝜔𝑣0 cos 𝜔𝑡
=
𝑣0
1
𝐶𝜔
cos 𝜔𝑡 =
𝑣0
𝑋𝑐
𝑠𝑖𝑛 90 + 𝜔𝑡 = 𝑖0sin(90 + 𝜔𝑡)
𝑣 = 𝑣0𝑆𝑖𝑛𝜔𝑡 𝑎𝑛𝑑 𝑖 = 𝑖0𝑆𝑖𝑛(90 + 𝜔𝑡)
Hence in a capacitor, current leads voltage by 90°
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9. Capacitive reactance
Capacitors block dc and provide an opposition to current flow to ac signals
Opposition to ac signal is its reactance
𝑋𝑐 =
1
𝜔𝐶
=
1
2𝜋𝑓𝐶
𝑋𝑐 - reactance expressed in ohms,
𝑓 - frequency of input signal in Hz
C - capacitance value in farads
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10. Q factor
• Capacitors are basically energy storing elements
• Quality of a capacitor is expressed in terms of a parameter called quality factor (Q)
𝑄 =
2𝜋 × 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑒𝑛𝑒𝑟𝑔𝑦 𝑠𝑡𝑜𝑟𝑒𝑑
𝐸𝑛𝑒𝑟𝑔𝑦 𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑒𝑑 𝑝𝑒𝑟 𝑐𝑦𝑐𝑙𝑒
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑒𝑛𝑒𝑟𝑔𝑦 𝑠𝑡𝑜𝑟𝑒𝑑 =
1
2
𝐶𝑉
𝑚
2
𝐸𝑛𝑒𝑟𝑔𝑦 𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑒𝑑 =
𝑉
𝑚
2
2𝑅
𝐸𝑛𝑒𝑟𝑔𝑦 𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑒𝑑 𝑝𝑒𝑟 𝑐𝑦𝑐𝑙𝑒 =
𝑉𝑚
2
2𝑓𝑅
Value of R for an ideal capacitor is infinity and hence Q is also infinity
Higher the quality factor better the quality of capacitor
∴ 𝑸 = 𝟐𝝅𝒇𝑹𝑪 = 𝝎𝑹𝑪
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11. Capacitors are used in circuits
For blocking dc voltage
For coupling various stages of cascaded amplifiers
 As a bypass element in amplifiers
As filters in power supplies
For charge storage
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12. Specifications of Capacitors
Capacitance value
• Value of capacitor expressed in farads Either printed or indicated by colour coding
Voltage rating
• Maximum continuous voltage either DC or AC that can be applied to the capacitor
without failure
 Frequency range
• Range of frequency over which the capacitor can be used
Tolerance
• Deviation from the rated value
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13.  Temperature Coefficient of a capacitor
• The Temperature Coefficient of a capacitor is the maximum change in its capacitance
over a specified temperature range. The temperature coefficient of a capacitor is generally
expressed linearly as parts per million per degree centigrade (PPM/oC), or as a percent
change over a particular range of temperatures
Dielectric constant of the dielectric material changes with temperature
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14. Six dot code
Colour and Number Code of Capacitors
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15. Electrolytic Capacitors:
There are two designs of electrolytic capacitors:
(i) Axial where the leads are attached to each end (220µF in picture)
(ii) Radial where both leads are at the same end (10µF in picture).
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16.  If the number written on the capacitor is greater than one, the value will be
in pF. Otherwise, it will be in μF. For example, 10 means 10 pF and 0.1
means 0.1 μF.
 If there are three digits in the number, the third number indicates the
number of zeros to be put after first two digits and the value will be in pF.
104 means 10,0000 pF or 0.1 μF
 If the letter k follows the digits, the value will be in kpF (kilo picofarad). 10
k means 10 kpF or 0.01 μF.
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17.  If the letter is ‘n’ or ’M’ the value will be that much nano farads or micro
farads respectively. 47n means 47 nF and 47M means 47 μF.
 If the letter n, M or k is between two numerals, the value of the capacitor
can be obtained by putting a decimal in place of the letter and multiplying
by the factor nF, μF or kpF respectively.
4k7 means 4.7 kpF and 2M2 means 2.2 μF.
 If the letters k or M follows the three digit number, it implies the tolerance
value 10% and 20% respectively.
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18. SIX DOT CODE
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19. Colour bands
Sometimes capacitors just show bands like resistors when printing is
tough on them.
The colours should be read like the resistor code, the top three colour
bands giving the value in pF.
The 4th band and 5th band are for tolerance and voltage rating
respectively.
For example: brown, black, orange means 10000pF = 10nF = 0.01µF.
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20. Colour Coding of Capacitors
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21. Standard Values of Capacitor
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22. Classification of capacitors
Types of Capacitors:
Fixed Capacitors
Variable Capacitors
Fixed Capacitors
Paper Capacitors
Mica Capacitors
Ceramic Capacitors
Electrolytic capacitors
Polyster capacitors
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Capacitor Symbols

23. Mica capacitors
Mica sheets are brittle and cannot be rolled up like a paper dielectric
Mica is used as dielectric sheet and must be free from holes, uniformly thick and without
cracks or folds.
Made from plates of aluminium foil separated by sheets of mica
Constructed by interleaving thin films of mica with foils of tin or aluminium.
By connecting alternate foils, two sets of metal plates are formed to which separate terminals
are connected.
The complete unit is enclosed in a moulded ceramic or bakelite case with terminals coming out
at each end
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24. Mica Capacitor
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Available capacitances range from 5 to 10,000 pF

25. Mica capacitors
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Features
 Small capacitance value
 High voltage rating (200V to 1000V)
 Low loss factor
 Less leakage current
 High stability
 Suitable for high frequency operation
Applications - filtering, tuning, bypassing

26. Paper capacitors
• Consists of two metal foils separated by strips of paper
• This paper is impregnated with a dielectric material such as wax, plastic or oil.
•
• The foil and paper are then rolled in the form of a cylinder and wire leads are
attached
• Paper capacitors vary from 0.0005mF to 2µF with voltage rating up to 1000V
• They have longer life and can be used in both dc and ac circuits
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27. Fig. 5: Paper Capacitor
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Paper Capacitor

28. Ceramic capacitors
 Available in many shapes and sizes (like disc, tubular and button type)
 A ceramic disc is coated on two sides with a metal, such as copper or
silver. These coatings act as two plates. After attaching tinned-wire leads,
the entire unit is coated with plastic .
 Ceramic capacitors are available in the range of 3pF to 2µF
 working voltage ranges from 3 V up to 6000 V
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29. Ceramic Capacitor
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30. Electrolytic capacitors
Generally used in applications where very large capacitance values are required
These capacitors have a metallic positive plate on which a thin layer of oxide is grown
electrochemically to act as dielectric (anodization)
The oxide is in contact with a paper or gauze saturated with an electrolyte. The
electrolyte forms the second plate (negative) of the capacitor.
These capacitors arecalled electrolytic becausethey use an electrolyte as negative plate
Another layer of aluminium without the oxide coating is also provided for making
electrical contact between one of the terminals and the electrolyte.
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31.  In most cases, the negative plate is directly connected to the metallic
container of the capacitor. The container then serves as the negative
terminal for external connections.
 Categorized according to their dielectric material
• Aluminium electrolytic capacitors - Aluminium oxide acts as dielectric
• Tantalum electrolytic capacitors - Tentalum pentoxide acts as dielectric
• Niobium electrolytic capacitors - Niobium pentoxide acts as dielectric
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32.  Most of these capacitors have polarity, so it must be carefully connected to the
circuit based on polarity
 Aluminium electrolyte capacitors - 1μF - 1000μF, 400V ,10Hz to 10KHz
 For tantalum capacitors - 1μF - 10000μF , 75V, 10Hz to 10KHz
• Stability is high
• Leakage current is low
• Cost of fabrication is high
 Aluminium capacitors are commonly used as it is available in high voltage rating
and cost of fabrication is less
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33. Electrolytic Capacitor
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34. Polyster Capacitor
• In polyester capacitor dielectric used is polyster.
• It consist of two metal foil separated by a strip of polyester material such
as Mylar.
• Voltage rating upto 400V
• Capacitance 100pF - 2µF
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35. Variable capacitors
• These capacitors are designed so that the capacitance value is variable within
the limits
• Capacitance variation can be achieved by the following principles
 Mechanically variable capacitor
 Electrically variable limits
 Thermally variable capacitors
 Optically variable capacitors
• Used in radio receivers and transmitters for tuning
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36. Gang Capacitors
• Capacitance is varied by varying the overlapping area between two sets of plates
• Air is the dielectric
• One set remain stationary and is called stator
• The other set of plates can be rotated by means of a shaft and is called rotor
• By rotating the shaft at one end, we can change the common area between the
movable and fixed set of plates
• The greater the common area, the larger the capacitance.
• The capacitance value is in the range of pF to nF
• Used in radio tuning circuits, signal generators etc. Basics of Electrical and Electronics Engineering 36 / 44

37. Gang Capacitor
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38. Trimmers
• In some applications, the need for variation in the capacitance is not frequent. One
setting is sufficient for all normal operations. In such situations, we use a variable
capacitor called a trimmer (sometimes called padder).
• Both mica and ceramic are used as the dielectric for trimmer capacitors.
• They are mechanically variable capacitors in which the distance between the electrodes is
varied to obtain variation in capacitance
• The movable plate is of spring material which can be moved closer to or away from the
fixed plate by means of a screw
• They are small value capacitors (3-30 pF, 4-70pF)
• Used in conjunction with large capacitors for fine adjustments
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39. Trimmers
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40. Padders
• Almost same as trimmer
• It has large size and large capacitance values (400-600pF, 750-1000pF)
• Used in tuning circuits
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41. Padders
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