Basic Electronics On The Go - Capacitor Color Codes

Introduction

Capacitance of a capacitor is the ability of a capacitor to store maximum charge on its plates. The capacitance of a capacitor is measured in the units of Farads. Generally the capacitance values, working voltage and tolerance values are indicated on the body of a capacitor.

But sometimes it is difficult to identify these capacitance and voltage values on the capacitor body in the case of decimal values. It also causes misreading of the actual capacitance and voltage values. So , a technique was used to identify the capacitance values by using the letters like p (pico) and n (nano) instead of decimal values (such as 200 k=200*1000 pF=200 nF and 47 n=47 nF,  n47=0.47nF etc).

So to avoid these problems a color scheme was introduced for capacitors like resistors. This colour scheme for capacitors is usually called  capacitor color coding. In this scheme each color of a capacitor indicates a specific capacitance value. Using this color scheme we can easily identify the capacitance values, voltages and tolerance values of any capacitor. These color schemes, color coding and colors assigned for values are explained  below.

Table :Capacitor Voltage Color Code

Capacitor Voltage Reference

The capacitor has the capacitance value, voltage , tolerance and manufacturer numbers on the body of a capacitor. Some voltage values are used as references for working voltages of a capacitor. In this representation we see some letters or characters like J, K, N, M etc. Now let us the meaning of those letters which are used on the body of a capacitor.

J-Type => Dipped Tantalum type capacitors

K-Type => Mica type capacitors

L-Type +> Polyester (or) Polystyrene type capacitors

M-Type => Electrolytic 4 Band type capacitors

N-Type => Electrolytic 3 Band type capacitors

Metalized Polyester Capacitor

Figure 1.Metalized Polyester Capacitors with color codes

The capacitors which are shown in the above figure are metalized polyester capacitors with color codes. In this each color represents a specific parameter for capacitance values, tolerance and working voltages. All the above capacitors have different capacitance and tolerance values.These values can be understood by the color code table which is given at the side of capacitors in the above figure.

Disc & Ceramic Capacitor

The above figure shows the Disc and Ceramic capacitors with color codes. These colour codes are used for many years for non-polarized capacitors like disc and ceramic capacitors. But it is difficult to identify the values in the case of old capacitors. So these old capacitors are now replaced with new numbers.

In three digit number representation , the third number represents number of zeros, such as 471=470pF, 101=100pF. In the case of two digit number representation tolerance is also identified. In two number representation, disc or film capacitors have the capacitance value usually in pico-Farads, for example 47=47pF, 20=20pF. In the above figure we observe that  the capacitance values and tolerance for small disc or large disc capacitors can be calculated by using the color code which is shown at the side of capacitors.

Capacitor Tolerance Letter Codes Table

Capacitor has numbers and letters on its body to identify the capacitance values and tolerance values respectively.Letters for the specific tolerance value representation is shown in the below table. Now we will see one example to understand this concept below.

The capacitor which is shown in the above figure has 473 J code on its body. Here 4 is first digit, 7 is second digit and 3 is the number of zeros i.e. the capacitance value is 47*1000pF=47000pF=47nF=0.047uF. Here letter ‘J’ denotes the tolerance of a capacitor, referring to above table , tolerance of this capacitor is +/-5%. In this way by just using numbers and letters on the body of a capacitor, we can easily determine the capacitance values and tolerances of capacitors.

Table:Capacitor Letter Codes

The capacitance values of capacitor are  measured in pico-Farads, nano-Farads, or micro-Farads. The relation between these values for different letter codes is shown in the above table. From this table we clearly can understand about the units of capacitance. The basic relation between them is 1uF=1000nf=1000000pF

Basic Electronics On The Go -Capacitors in Series and Parallel

From http://www.electronicshub.org/capacitors-in-series-and-parallel/

Capacitors in series

Capacitors in series meanstwo or more capacitors are connected in a single line i.e positive plate of the one capacitor is connected to the negative plate of the next capacitor. All the capacitors in series have equal charge (Q) and equal charging current (iC).

Consider N- numbers of capacitors are connected in series, then

QT =Q1 = Q2 = Q3 = ———- = QN

IC = I1 = I2 = I3 = ——— = IN

Capacitors in a Series Connection

The following circuits show the series connection of group of capacitors.

series connection of N-number of capacitors.

series connection of two capacitors.

In this circuit the charge (Q) stored in all capacitors is same because every capacitor has the charge which is flowing from the adjacent capacitor. The voltage drop in all capacitors is different from each other. But the total voltage drop applied between input and output lines of the circuit is equal to the sum of all the individual voltage drops of each capacitor. The equivalent capacitance of the circuit is Ceq = Q/V.

Thus,

VT = V1 + V2

Ceq = Q/V1 + Q/V2

1/Ceq = (V1+ V2)/Q

VT = Q/Ceq = Q/C1 + Q/C2

Series Capacitors Equation

1/Ceq = 1/C1 + 1/C2 +……… + 1/CN

When the capacitors are in series connection the reciprocal of the equivalent capacitance is equal to the sum of the reciprocals of the individual capacitances of the capacitors in the circuit.

From the figure 2, the reciprocal of equivalent capacitance value of the circuit is equal to the sum of reciprocal capacitances values of two capacitors C1 and C2, the expression is given below.

1/Ceq = 1/C1 + 1/C2

Capacitors in Parallel Circuits

Capacitors in parallel means two or more capacitors are connected in parallel way, i.e. both of their terminals are connected to each terminal of the other capacitor or capacitors respectively. All the capacitors which are connected in parallel have the same voltage and is equal to the VT applied between the input and output terminals of the circuit. Then, parallel capacitors have a ‘common voltage’ supply across them .i.e. VT = V1 = V2 etc.

Parallel connection of two capacitors

In  above figure  the total charge (Q) across the circuit is divided between the two capacitors, means the charge Q distributes itself between the capacitors connected in parallel. Because the voltage drop across individual capacitors is equal and also it is equal to the total voltage applied to the circuit. But the total charge Q is equal to the sum of all the individual capacitor charges connected in parallel. i.e. From the above figure the two different capacitors C1 and C2 have two different charges Q1 and Q2 respectively. Here Q=Q1+Q2

Now we see the equivalent capacitance of the capacitors C1 and C2 connected in parallel which shown in  the above figure.

We know the formula,

Q=Ceq VT

Here, Q = Q1+Q2

And VT = V1 = V2

Ceq=Q/VT = (Q1+Q2)/VT = (Q1/VT) + (Q2/VT)

Parallel Capacitors Equation

Ceq = C1+C2+C3+ ———— +CN

The equivalent capacitance of the capacitors which are connected in parallel is equal to the sum of the individual capacitances of the capacitors in the circuit.

From the figure 4, the equivalent capacitance (Ceq) value is equal to the sum of both the capacitance values of C1 and C2, the expression is shown below.

Ceq = C1+C2

Basic Electronics On The Go -Capacitive Voltage Divider

From http://www.electronicshub.org/capacitive-voltage-divider/

Introduction

In a voltage divider circuit,the supply voltage or circuit voltage is distributed among all the components in the circuit equally,depending on the capacity of those components.

The construction of capacitive voltage divider circuit is the  same as the resistive voltage divider circuit. But like resistors, the capacitive voltage divider circuit is not affected by the changes in the frequency even though it uses reactive elements.

The capacitor is a passive component which stores electrical energy in the metal plates. A capacitor has two plates and these two are separated by non-conducting or insulating material, such as called as “dielectric”.

Here the positive charge is stored on one plate and negative charge is stored on another plate.

When DC current is applied to the capacitor, it charges fully. The dielectric material between the plates acts as insulator and also it opposes the current flow through the capacitor.

This opposition to supply current through the capacitor is called reactance (XC) of a capacitor. The capacitor reactance is also measured in ohms.

A fully charged capacitor acts as an energy source, because a capacitor stores energy and discharges it to the circuit components.

Voltage Distribution in Series Capacitors

If the capacitors are connected in series , the voltage distribution between the capacitors is calculated. Because the capacitors have different voltage values depending on the capacitance values in series connection.

The reactance of a capacitor which opposes the flow of current , depends on the value of capacitance and frequency of the applied current.

So now let us see how the reactance affects the capacitors , by calculating the frequency and capacitance values. Below circuit shows the capacitive voltage divider circuit in which 2 capacitors are connected in series.

Capacitive Voltage Divider

The two capacitors which are connected in series have the capacitance values of 10uF and 22uF respectively. Here the circuit voltage is 10V,this voltage is distributed between both capacitors.

In the series connection all the capacitors have same charge (Q) on it but the supply voltage (VS) is not same for all capacitors.

The circuit voltage is shared by the capacitors depending on the capacitance values of the capacitors.i.e. in the ratio of V = Q/C.

From these values we have to calculate the reactance (XC) of each capacitor by using frequency and capacitance values of capacitors.

Capacitive Voltage Divider Example No1

Now we will calculate the voltage distribution to the capacitors 10uF and 22uF which are given in the above figure which have 10V supply voltage with 40HZ frequency.

Reactance of 10uF capacitor,

XC1 = 1/2πfC1 = 1/(2*3.142*40*10*10-6) = 400Ω

Reactance of 22uF capacitor,

XC\2 = 1/2πfC2 = 1/(2*3.142*40*22*10-6) = 180Ω

Total capacitive reactance of a circuit is,

XC= XC1+ XC2= 400Ω + 180Ω = 580Ω

CT= C1C2/(C1+C2) = (10*22*10-12)/(32*10-6) = 6.88uF

XCT = 1/2πfCT = 1/(2*3.142*40*6.88*10-6) = 580Ω

The current in the circuit is,

I = V/XC = 10V/580Ω = 17.2mA

Now, the voltage drop across each capacitor is,

VC1 = I*XC1 = 17.2mA*400Ω = 6.9V

VC2 = I*XC2 =17.2mA*180Ω = 3.1V

Summary

• The opposition for the flow of current in the capacitor is known as reactance (XC) of a capacitor. This capacitive reactance is influenced by the parameters like capacitance value,frequency of supply voltage and also these values are inversely proportional to the reactance.
• The AC voltage divider circuit will distribute the supply voltage to all the capacitors depending on their capacitance value.
• These voltage drops for the capacitors are same for any frequency of supply voltage. i.e. the voltage drops across capacitors are independent on frequency.
• But the current flowing is depending on frequency and also these two are directly proportional to each other.
• But in DC voltage divider circuits, it is not an easy task to calculate the voltage drops across capacitors as it depends on reactance value, because the capacitors block DC current flow through it after fully charged.
• The capacitive voltage divider circuits are used in large electronics applications.Mainly used in capacitive sensitive screens those change their output voltage when it is touched by a person's finger.
• And also used in transformers to increase voltage drop where generally the mains transformer contains low voltage drop chips and components.
• Finally one thing to say is in voltage divider circuit the voltage drops across capacitors are same for all frequency values.

Basic Electronics On The Go - Capacitance in AC Circuits

From http://www.electronicshub.org/capacitance-in-ac-circuits/

Introduction

When DC supply voltage is applied to the capacitor,the capacitor is charged slowly and finally it reaches to fully charged position. At this point the charging voltage of a capacitor is equal to the supply voltage. Here the capacitor acts as an energy source as long as voltage is applied. Capacitors don’t allow current (i) through them after they are fully charged.The current flowing through the circuit depends on the amount of charge in the plates of capacitors and also the current is directly proportional to the rate of change of voltage applied to the circuit. i.e. i = dQ/dt = C dV(t)/dt.

If AC supply voltage is applied to the capacitor circuit then the capacitor charges and discharges continuously depending on the rate of frequency of supply voltage.  In AC circuits the capacitors allow current when the supply voltage is continuously changing with respect to time.

AC Capacitor Circuit

In the above circuit we observed that a capacitor is directly connected to the AC supply voltage. Here the capacitor continuously charges and discharges depending on the changes in supply voltage, because the AC supply voltage value is constantly increasing and decreasing. We all know that the current flowing through the circuit is directly proportional to the rate of change of voltage applied.

Here the charging current has its high value, if the supply voltage crosses its value from positive half cycle to the negative half cycle and vice versa. i.e. at  00 and 1800 in sine wave signal. The current through the capacitor has its minimum value when the supply voltage in sine wave crosses over at its maximum or minimum peak value (Vm). Hence we can say that the charging current flowing through the circuit is maximum or minimum depending on the supply voltage levels in sine wave.

AC Capacitor Phasor Diagram

The phasor diagram of AC capacitor is shown in the above figure, here the voltage and currents are represented in sine wave forms. In the above figure we observed that at 00 the charging current is at its maximum value because the voltage is increasing slowly in positive direction. At 900 there is no current flow through the capacitor because at this point the supply voltage is at its maximum peak value.

At 1800 point the voltage slowly decreases to zero and current is at maximum value in the negative direction. Again the charging reaches to its maximum value at 3600, because at this point the supply voltage is at minimum value.

From the waveforms in the above figure we can see that, the current is leading the voltage by 900. Hence we can say that in an ideal capacitor circuit the AC voltage lags the current by 900.

Capacitive Reactance

We know that the current flowing through the capacitor is directly proportional the rate of change of applied voltage but capacitors also offer some form of resistance against the current flow same as like resistors. This resistance of capacitors in AC circuits is called  capacitive reactance . Capacitive reactance is the property of a capacitor which opposes the flow of current in AC circuits. It is represented with symbol Xc and measured in Ohms same as like resistance.

We need some extra energy over capacitive reactance to charge up a capacitor in the circuit. This value is inversely proportional to the capacitance value and the frequency of supply voltage.

Xc∝ 1/c and Xc∝ 1/f.

The equation for capacitive reactance and parameters which influences them are discussed below.

Capacitive Reactance,

X_C = 1/2πfC = 1/ωC

Here,

X_C = Reactance of capacitor

f = frequency in HZ

C = Capacitance of a capacitor in Farads

ω (omega) = 2πf

From the above equation we understood that capacitive reactance is high where the frequency and capacitance values are at low and at this stage the capacitor acts as a perfect resistor. If the frequency of supply voltage is high then the reactance value of capacitor is low and also at this stage capacitor acts as a good conductor. From the above equation it is clear that the reactance is zero if the frequency is infinity and the reactance value is infinity where the frequency is at zero.

Capacitive Reactance against Frequency

The above figure shows the relation between the capacitive reactance, current and frequency of the supply voltage. Here we observed that if frequency is low then the reactance is high. The charging current increases with increase in frequency, because the rate of change of voltage increases with time.The reactance is at infinite value where the frequency is zero and vice versa.

AC Capacitance Example No1

Find the rms value of current flowing through the circuit having 3uF capacitor connected to 660V and 40Hz supply.

Capacitive Reactance,

XC = 1/2πfC

Here,

f = 40HZ

C = 3uF

Vrms = 660V

Now,

XC = 1/(2 × 3.14 × 40HZ  × 3 × 10-6) = 1326Ω

Irms = Vrms/XC = 660V/1326Ω = 497mA

Basic Electronics On The Go - Applications of Capacitors

From http://www.electronicshub.org/applications-of-capacitors/

Introduction

Capacitor is one of the passive components and it stores energy in the form of electrical charge. Capacitor charges and discharges the charge depending on the circuit operation. It is used mainly in electronic and electrical circuits to perform different tasks, such as smoothing, filtering, bypassing, noise reduction, sensing capabilities  etc.

 First of all we need to choose which type of capacitor is suitable for a particular application. Choosing of capacitor type depends on some factors. The factors which influences in choosing type of a capacitor for a specific application are given below,

Capacitance Value Ranges: Each type of capacitor available in a specific range. Depending on application we need to choose a required range of capacitor.

Working Voltage:Some types of capacitors have low working voltages and some more type of capacitors have high working voltages. Depending on the application we need to choose the capacitor voltage.

Polarization:Tantalum and electrolytic capacitors are polarized and also they operate with a voltage in one direction. So polarization is one of the important factors while choosing the capacitor.

Tolerance: The close tolerance value capacitors are needed to choose for applications like oscillators and filters where the capacitor value is critical. But in some type of applications like coupling and de-coupling the value of capacitor is not critical.

Temperature Coefficient:Capacitance value varies with temperature in some type of capacitors and some capacitors like silver mica, ceramic are stable with varying temperatures. So depending on application one can select the capacitor.

Leakage Current: High level insulation is needed in some applications but in some applications it is not necessary. Electrolytic capacitors have poor leakage performance. Leakage current is also considerable factor while choosing the capacitor for application.

Cost: The cost is the basic driving parameter for all applications. Because everyone want to have high performance with low cost.Today, all the high performance capacitors are available for low cost in surface mount packages.

Table of capacitor applications

(click on table to see bigger view)

Filter Applications

Capacitors are used as main elements in frequency selective filters. All the filter designs are used for the high performance and frequency based applications,by selecting the proper components and quality required. Some of the filter topologies are given below.

•  High Pass Filter (HPF)
•  Low Pass Filter (LPF)
•  Band Pass Filter (BPF)
•  Band Stop Filter (BSF)
•  Notch Filter (NF)
•  All Pass filter (ALF)
•  Equalization Filter (EF)

Decoupling/By-Pass Capacitors

Decoupling capacitors are used in digital electronics to protect the microchips from the electrical noise on power signals. The main role of decoupling capacitors is to reduce the noise in the circuit. These capacitors are placed very close to the microchips in the circuits to remove noise from the surroundings. These capacitors are also provides extra energy to the IC’s and also remove disturbances to the logic signal.

Coupling or DC Blocking Capacitors

The coupling or DC blocking capacitors are used in the applications where the AC and DC signals  need to be separated. These types of capacitors will allow only AC signals and blocks the DC signals. Here the capacitance value of a capacitor will not affect the coupling applications. But the performance of these capacitors is high in the applications if the reactance of a capacitor is high value. The main use of these capacitors is to block the DC currents from the signal. These types of capacitors are used to pass AC signals for coupling of one electronic circuit to another circuit.

Snubber Capacitors

Snubber capacitors are used in the circuits where high inductance load is driven. In high inductance circuits, such as in transformers and in motors the stored energy is discharged suddenly. Due to this effect other components in the circuit may damage and also large power spikes are obtained in those circuits. To avoid these problems we use capacitors across the high inductive components in the circuits.Due to this process the capacitors avoid voltage spikes and also they provide safety to the circuit.

Low power circuits also use these snubber capacitors to avoid voltage spikes, which are created from undesirable radio frequency (RF) interferences.These snubber capacitors are also used in parallel to the interrupt components, in the high voltage circuits to avoid circuit breaker problems by producing equal voltage distribution between those components.

Pulsed Power Capacitors

Generally a capacitor is small energy storage component. Large capacitors and capacitor banks are used where a lot of energy required within a short period of time. Capacitor banks store the lot of energy for the applications, such as particle accelerators, pulsed lasers, radars, max generators, fusion research and rail guns. A normal application for pulsed power capacitors is used in a flash on disposable camera which charges up and discharges quickly through its flash.

Resonant or Tuned Circuit Applications

To design filters we use capacitor, resistors and also inductors. In this design some combinations of components are used, to amplify the resonant frequency signals. Here the low power signals are amplified to the high power signals, at resonant frequency, as tuned filters or oscillators. But in designing the resonant frequency circuits we take much care about the component combinations because some of the combinations  may damage the operation and also fail quickly.

Capacitive Sensing Application

The capacitive sensing is a technique in detecting the change in capacitance value, change in the distance between the plates, change in dielectric and change in the area of capacitor plates. Capacitive sensing is a technique which is recently used in advanced consumer electronic circuits. Capacitive sensors are used in different applications such as position, fluid level, humidity, acceleration and manufacturing quality control etc.

Capacitor Safety

We need to take some safety precautions about capacitors. Capacitors are storage devices, which store electrical energy from small amounts to large amounts. Due to this high energy we can observe electrical charge even though the power is disconnected. Sometimes these high energy capacitors may damage the circuit components. The best thing to avoid these problems is to discharge the capacitors before use in the electrical circuits.

If the voltage to the polarized electrolytic capacitors are reversed then these capacitors may fail in the circuit operations. The breaking of dielectric material also causes failure of the capacitors even though they are used in high voltage and high power applications.

Basic Electronics On The Go - Capacitors

From http://www.electronicshub.org/introduction-to-capacitors/

Introduction to Capacitor

What is Capacitor?

Capacitor is also known as condenser. This is one of the passive components like a  resistor. Capacitor is generally used to store the charge. In capacitor the charge is stored in the form of “electrical field”. Capacitors play a major role in many  electrical and electronic circuits.

Generally, a capacitor has two parallel metal plates which are not connected to each other. The two plates in the capacitor are separated by non conducting medium (insulating medium) this medium is commonly known as Dielectric.

There are different types and different shapes of capacitors  available , from very small capacitors which are used in resonance circuits to large capacitors for  stabilising HVDC lines. But all capacitors are doing the same work that is storing the electrical charge.

The shape of a capacitor is rectangular, square, circular, cylindrical or spherical shape. Unlike a resistor, an ideal capacitor does not dissipate energy.As the different types of capacitors are available different symbols were available to represent them which are shown below.

Why capacitors are important?

Capacitors have many properties like

1. They can store the energy and it can dissipate this energy to the circuit when ever required.
2. They can block DC and allow AC to flow through it, and this can couple one part of the circuit with the other.
3. Circuits with capacitors depend on the frequency, so they can be used to amplify certain frequencies.
4. For capacitors when applied with AC input , the current leads the voltage and thus in power applications it increases the pay load power and makes it more economical.
5. It allows high frequencies and so it can be used as a filter either to filter low frequencies or to collect high frequencies.
6. As the reactance and frequency of the capacitor are inversely related, this can be used to increase or decrease the circuit impedance at certain frequency and can be used as filter.

Likewise, capacitors exhibit many properties , when used in AC or DC circuits and hence they play important role in electrical and electronic circuits.

Construction of a Capacitor

As said before , there are different types of capacitors. These different types will have different type of construction. A Parallel plate capacitor is the simplest capacitor. Let us understand the construction of this capacitor.

It consists of two metal plate separated by a distance. The space between these two plates is filled with a dielectric material. The two leads of the capacitor are taken from these two plates.

The capacitance of the capacitor depends on the distance between the plates and area of the plates. Capacitance value can be changed by varying any of these parameters.

A variable capacitor can be constructed by making one of these plates fixed and other moving.

Dielectric Of a Capacitor

Dielectric acts as an insulating material between the plates . Dielectric can be any non conducting material such as ceramic, waxed paper, mica, plastic or some form of a liquid gel.

Dielectric also plays an important in deciding the value of capacitance.

Different dielectric materials will have different dielectric constants ,however this value is >1.

The table  gives the value of dielectric constant (relative permittivity) for each dielectric material

Dielectric can be of two types

1. Polar dielectrics: These dielectrics will have permanent dielectric moment
2. Non Polar dielectrics: These will have temporary dielectric moment. By placing them in a electric field they can be induced with dipole moments.

Absolute Permittivity

The product of the relative permittivity (εr) of the dielectric material and permittivity of free space (εo) is known as absolute permittivity. The expression for the absolute permittivity is given as follows,

ε = ε0 * εr

Some standard values of relative permittivity  or dielectric constant for common dielectric materials are Air = 1.0005, Pure Vacuum = 1.0000, Mica = 5 to 7, Paper = 2.5 to 3.5, Wood = 3 to 8, Glass = 3 to 10 and Metal Oxide Powders = 6 to 20 and etc.

Capacitors can be classified according to the properties and characteristics of their insulating or dielectric material, they are given below as

1. High Stability & Low Loss Capacitors — Mica, Low-K Ceramic, and Polystyrene capacitors are examples for this type.
2. Medium Stability & Medium Loss Capacitors – Paper, Plastic Film, and High-K Ceramic capacitors are examples for this type.
3. Polarized Capacitors – Example for this type of capacitors are Electrolytic, Tantalum’s.

Working

As said before capacitor consists of two conductor separated by a dielectric . When there is any potential difference between the two conductors electric potential is developed.This causes the capacitor to charge and discharge.

Let us understand this in a  practical way. When the capacitor is connected to a battery(a DC source) , current starts flowing through the circuit .

Thus negative charge is accumulated on one plate and positive charge is accumulated on the other plate. This process continuous until the capacitor voltage reaches supply voltage.

When the charging voltage is equal to the supply voltage, the capacitor stops charging further even though the battery is connected. When the battery is removed two plates will be accumulated with positive and negative charges. Thus the charge is stored in the capacitor.

But when the supply voltage is from an AC source it charges and discharges continuously .The rate of charging and discharging depends on the frequency of the source. 

Capacitance of a Capacitor

The capacitance of a capacitor is

C = εo * εr (A/d)

Where,

C – Capacitance of the capacitor

A – Area between the plates

D – Distance between the two Plates

εo – Permittivity of free space

εr – Relative permittivity.

Capacitance is the property of the capacitor that defines the maximum amount of electrical charge stored in it.

Capacitance may vary depending on the shape of the capacitor. Capacitance can be calculated by using the geometry of the conductors and dielectric material properties. Let us see the capacitance of a parallel plate capacitor.

Capacitance is defined as the ratio of charge (Q) on the either plates to the potential difference(V) between them ,

                               C =Q/V,

Current can be obtained as

I(t)=C[d(v)/d(t)]

This can can be expressed Farads (F) which is named after English physicist Michael Faraday.

From the above definition we can observe that capacitance is directly proportional to the charge (Q) and is inversely proportional to the voltage (V).

Capacitance of the capacitor can be increased by increasing the number of plates, which helps to maintain the same size of the capacitor. Here, area of the plates is increased.

Standard units of capacitance

Generally Farads is a high value so, capacitance is expressed as sub units of capacitor real time such as as micro farads(uF) , nano farads(nF) and pico farads(pF).

Most of the electrical and electronic applications are covered by the following standard unit (SI) prefixes for easy calculations,

• 1 mF (milli farad) = 10^−3 F = 1000 μF = 1000000 nF
• 1 μF (microfarad) =10^−6 F = 1000 nF = 1000000 pF
• 1 nF (nano farad) = 10^−9 F = 1000 pF
• 1 pF (picofarad) = 10^−12 F

To convert µF to nF or pF or to a wide range of other units and vice versa, we need to use the Electric Capacitance Unit Converter.

Voltage Rating of a Capacitor

This is not voltage until which the capacitor charges but the maximum voltage until which the capacitor can operate safely. This voltage is called as working voltage (WV) or DC working voltage (DC-WV).Below figure shows the voltage rating of the capacitor.

If the capacitor is applied with voltage greater than this voltage, it may be damaged by producing an arc between the plates due to dielectric break down.

While designing the circuits with capacitors, care should be taken such that the voltage rating of the capacitor is greater than the voltage used in the circuit. For example if the circuit operating voltage is 12V then it is necessary to choose a capacitor with voltage rating of 12V or above.

This working voltage of a capacitor depends on the factors like dielectric material used between the capacitor plates, dielectric thickness and also on the type of circuit which is used.