Friday 13 January 2017

Voltage, Current, and Resistance Relate Ohm's Law


Voltage, Current, and Resistance Relate Ohm's Law



An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of “flow,” just like the flow of a liquid through a hollow pipe.
The force motivating electrons to “flow” in a circuit is called voltage. Voltage is a specific measure of potential energy that is always relative between two points. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point. Without reference to two particular points, the term “voltage” has no meaning.
Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. Just like voltage, resistance is a quantity relative between two points. For this reason, the quantities of voltage and resistance are often stated as being “between” or “across” two points in a circuit.

Ohm’s Law is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory by the serious student. For those who are not yet comfortable with algebra, there’s a trick to remembering how to solve for any one quantity, given the other two. First, arrange the letters E, I, and R in a triangle like this:
If you know E and I, and wish to determine R, just eliminate R from the picture and see what’s left:
If you know E and R, and wish to determine I, eliminate I and see what’s left:
Lastly, if you know I and R, and wish to determine E, eliminate E and see what’s left:
Eventually, you’ll have to be familiar with algebra to seriously study electricity and electronics, but this tip can make your first calculations a little easier to remember. If you are comfortable with algebra, all you need to do is commit E=IR to memory and derive the other two formulae from that when you need them!
  • REVIEW:
  • Voltage measured in volts, symbolized by the letters “E” or “V”.
  • Current measured in amps, symbolized by the letter “I”.
  • Resistance measured in ohms, symbolized by the letter “R”.
  • Ohm’s Law: E = IR ; I = E/R ; R = E/I

Tuesday 27 December 2016

CAPACITOR COLOR CODE CALCULATOR


Capacitor Color Coding


Capacitor Number Coding Chart


By referring to the above table, one can acknowledge the value of the capacitor, easily. Follow the below example for a better understanding. In the below example, the first two digits represent the first and the second significant digits (10) and the third one is a multiplier (2=100 as per table); and, alphabet represent tolerance (K= 10%) value as shown in the figure.
Capacitor Number Coding
Some more methods of finding the capacitor values include the following
1. The number printed on the capacitor’s body represents the capacitance value in Pico Farads.
For example, 8 =  8PF
2. If the third number is zero, then the value is in Picofarad
For example, 100 = 100PF
3. For a 3-digit value, the third digit represents the number of zeros after the second digit
For example,  104 = 10 – 0000 PF
4.  If the value is obtained in PF, then it is easy to convert it into KPF or uF
For example, PF / 1000 = KPF or, PF / 10, 00000 = uF. For a capacitance value of 104 or 100000 in pF, it is 100KpF or n or 0.1uF.
 5. For a 4-digit number, if the 4th number is a zero, then the capacitance value is in pF.
E.g. 1500 = 1500PF
6. If the number is a floating point decimal number, then the capacitance value is in uF.
E.g. 0.1 = 0.1 uF
7. If an alphabet is given between the digits, it represents a decimal and the value is in KPF
E.g. 2K2 = 2.2 KPF
8. If the values are represented with slashes, then the first digit represents value in UF, the second digit gives tolerance and the third represents maximum voltage rating.
E.g. 0.1/5/800 = 0.01 uF / 5 % / 800 Volt.


Capacitor Color Coding Value Calculator Chart
The first color is considered as the 1st digit in color chart, the second color band is  2nd digit, the third band is a multiplier, the 4th band is tolerance and the fifth color band is voltage rating of the capacitor. The capacitor color code chart is given below to identify the value of the capacitor


For example, consider the below capacitor wherein each color is represented with some value. The first band is orange that has value of 3 in the above chart, the second band is yellow 4, and the third one is 0.1 multiplier and the fourth band red is 0.25 tolerance.
Then its value is 34*0.1 pF with a tolerance of 0.25; finally, it is 3.4pF with a tolerance of 0.25 as shown in the figure.




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What is Capacitor?

Capacitor is a passive element that stores electric charge statistically and temporarily as an static electric field. It is composed of two parallel conducting plates separated by non-conducting region that is called dielectric, such as vacuum, ceramic, air, aluminum, etc.

The capacitance formula of the capacitor is represented by,
The capacitance formula of the capacitor is represented by,

C is the capacitance that is proportional to the area of the two conducting plates (A) and proportional with the permittivity ε of the dielectric medium. The capacitance decreases with the distance between plates (d). We get the greatest capacitance with a large area of plates separated by a small distance and located in a high permittivity material. The standard unit of capacitance is Farad, most commonly it can be found in micro-farads, pico-farads and nano-farads.
General uses of Capacitors


  1. Smoothing, especially in power supply applications which required converting the signal from AC to DC.
  1. Smoothing, especially in power supply applications which required converting the signal from AC to DC.

  1. Storing Energy.
  1. Storing Energy.

  1. Signal decoupling and coupling as a capacitor coupling that blocks DC current and allow AC current to pass in circuits.
  1. Signal decoupling and coupling as a capacitor coupling that blocks DC current and allow AC current to pass in circuits.

  1. Tuning, as in radio systems by connecting them to LC oscillator and for tuning to the desired frequency.
  1. Tuning, as in radio systems by connecting them to LC oscillator and for tuning to the desired frequency.

  1. Timing, due to the fixed charging and discharging time of capacitors.
  1. Timing, due to the fixed charging and discharging time of capacitors.

  1. For electrical power factor correction and many more applications.
  1. For electrical power factor correction and many more applications.

Charging a Capacitor
Capacitors are mainly categorized on the basis of dielectric used in them. During choosing a specific type of capacitors for a specific application, there are numbers of factors that get considered. The value of capacitance is one of the vital factors to be considered. Not only this, many other factors like, operating voltage, allowable tolerance stability, leakage resistance, size and prices are also very important factors to be considered during choosing specific type of capacitors.

Hence, it is cleared that, by varying ε, A or d we can easily change the value of C. If we require higher value of capacitance (C) we have to increase the cross-sectional area of dielectric or we have to reduce the distance of separation or we have to use dielectric material with stronger permittivity.

Types of Capacitors
The various types of capacitors have been developed to overcome these problems in a number of ways.

Paper Capacitor

It is one of the simple forms of capacitors. Here, a waxed paper is sandwiched between two aluminium foils.
Process of making this capacitor is quite simple. Take place of aluminium foil. Cover this foil with a waxed paper. Now, cover this waxed paper with another aluminium foil. Then roll up this whole thing as a cylinder. Put two metal caps at both ends of roll. This whole assembly is then encapsulated in a case. By rolling up, we make quite a large cross-sectional area of capacitor assembled in a reasonably smaller space.



We know that capacitance of a capacitor is given by,
If we go only for the increasing area of cross-section, the rise of the capacitor may become quite large; which may not be practically acceptable. Again if we reduce only the distance of separation, the thickness of dielectric becomes very thin. But the dielectric cannot be made too thin in case its dielectric strength in exceeded.
paper capacitor

Air Capacitor

There are two sets of parallel plates. One set of plates is fixed and another set of plates is movable. When the knob connected with the capacitor is rotated, the movable set of plates rotates and overlapping area as between fixed and movable plates vary. This causes variation in effective cross-sectional areas of the capacitor. Consequently, the capacitance varies when one rotates the knob attached to the air capacitor. This type of capacitor is generally used to tune the bandwidth of a radio receiver. variable air capacitor

Plastic Capacitor

When various plastic materials are used as dielectric material, the capacitors are said to be plastic capacitors. The plastic material may be of polyester, polystyrene, polycarbonate or poly propylene. Each of these materials has slightly different electrical characteristics, which can be used to advantage, depending upon the proposed application.
This type of capacitors is constructional, more or less same as paper capacitor. That means, a thin sheet one of the earlier mentioned plastic dielectrics, is kept between two aluminium foils. That means, here the flexible thin plastic sheet is used as dielectric instead of waxed paper. Here, the plastic sheet covered by aluminium foil from two sides, is first rolled up, then fitted with metal end caps, and then the whole assembly is encapsulated in a case.

Plastic Film Capacitor

Plastic capacitor can be made also in form of film capacitor. Here, thin strips or films of plastic are kept inside metallic strips. Each metallic strip is connected to side metallic contact layer alternatively; as shown in the figure below. That means, if one metallic strip is connected to left side contact layer, then the very next is connected to right side contact layer. And there are plastic films in between these metallic strips. The terminals of this type of capacitors are also connected to side contact layer and whole assembly is covered with insulated non metallic cover as shown. plastic capacitor

Silvered Mica Capacitor

A silvered mica capacitor is very accurate and reliable capacitor. This type of capacitors has very low tolerance. But on the other hand, cost of this capacitor is quite higher compared to other available capacitors in the market. But this high cost capacitor can easily be compensated by its high quality and performance. A small ceramic disc or cylinder is coated by silver compound. Here, electrical terminal is affixed on the silver coating and the whole assembly is encapsulated in a casing.

Ceramic Capacitor

Construction of ceramic capacitor is quite simple. Here, one thin ceramic disc is placed between two metal discs and terminals are soldered to the metal discs. Whole assembly is coated with insulated protection coating as shown in the figure below. Ceramic Capacitor

Mixed Dielectric Capacitor

The way of constructing this capacitor is same as paper capacitor. Here, instead of moving waxed paper as dielectric, paper impregnated with polyester is used as dielectric between two conductive aluminium foils.

Electrolyte Capacitor

Very large value of capacitance can be achieved by this type of capacitor. But working voltage level of this electrolyte capacitor is low and it also suffers from high leakage current. The main disadvantage of this capacitor is that, due to the use of electrolyte, the capacitor is polarized. The polarities are marked against the terminals with + and – sign and the capacitor must be connected to the circuit in proper polarity.
A few micro meter thick aluminium oxide or tantalum oxide film is used as dielectric of electrolyte capacitor. As this dielectric is so thin, the capacitance of this type of capacitor is very high. This is because; the capacitance is inversely proportional to thickness of the dielectric. Thin dielectric obviously increases the capacitance value but at the same time, it reduces working voltage of the device. Tantalum type capacitors are usually much smaller in size than the aluminium type capacitors of same capacitance value. That is why, for very high value of capacitance, aluminium type electrolyte capacitors do not get used generally. In that case, tantalum type electrolyte capacitors get used.
Aluminium electrolyte capacitor is formed by a paper impregnated with an electrolyte and two sheets of aluminium. These two sheets of aluminium are separated by the paper impregnated with electrolyte. The whole assembly is then rolled up in a cylindrical form, just like a simple paper capacitor. This roll is then placed inside a hermetically sealed aluminium canister. The oxide layer is formed by passing a charging current through the device, and it is the polarity of this charging process that determines the resulting terminal polarity that must be subsequently observed. If the opposite polarity is applied to the capacitor, the oxide layer is destroyed.
MaterialDielectric constantDielectric Strength Volts/.001 inch
Air180
Paper(Oiled)3-41500
Mica4-81800
Glass4-8200
Porcelain5750
Titanates100-200100

Monday 26 December 2016

Resistor Color Code Calculator

RESISTORS


Examples

3 bands:
Yellow, violet, black --> 47 ohm 20%
Orange, orange, brown --> 330 ohm 20%
Brown, black, red --> 1k 20%
4 bands:
Green, blue, red, gold --> 5.6kohm 5%
Red, yellow, orange, gold --> 24kohm 5%
Blue, gray, yellow, silver --> 680k 10%
More 4 band resistor color code examples: E12 and E24 series.
5 bands:
Red, yellow, orange, black, brown --> 243 ohms, 1% precision 5-band resistor
Yellow, violet, gold, gold, yellow --> 4.7 ohms, 5% - this resistor is calculated with the 4-band rule (the yellow band is ignored).
Orange, black, black, brown, brown --> 3.00 k ohms, 1% - note: this is a non-standard 1% (E96) resistor, but some manufacturers make every value from the E24 series with 1% tolerance!
6 bands:
Red, red, brown, brown, brown, red --> 2.21k, 1% 50ppm/°C
White, black, white, brown, red, red --> 9.09k, 2% 50ppm/°C
- do not enter the last band (red in the two examples above)

For standard precision resistors (four bands) : As mentioned above, standard precision resistors use four color bands. An image of the standard precision resistor is also shown above. For standard precision resistors,
  • The First band indicates the first digit of the resistance value.
  • The second band indicates the second digit of the resistance value.
  • The third band indicates the number of zeros to be added after the first two digits. Except when the color is silver or golden. Example 2 given below shows what should be done if the color is silver or golden.
  • The fourth band indicates tolerance.
What is a Resistor?
An electric resistor is a two-terminal passive component specifically used to oppose and limit current. A resistor works on the principle of Ohm’s Law which states that voltage across the terminals of a resistor is directly proportional to the current flowing through it.
Ohm’s Law: V = IR
where V is the voltage applied across resistor,
             I is the current flowing through it,
             and R is the constant called resistance.
The unit of resistance is ohms.

Types of Resistors:
Resistors can be broadly classified based on the following criteria: the type of material used, the power rating and resistance value.
1.        Fixed resistors.
2.    Variable Resistor

Fixed Resistor:
Types Of Fixed Resistor

Types of Resistors by Composition

There are 3 main types of resistors based on their composition: carbon-composition resistors, carbon-film resistors, and metal-film resistors.

Carbon-composition Resistors

Carbon-composition resistor
Carbon-composition resistors are resistors that are made of finely divided carbon or graphite mixed with a powdered insulating material as a binder in the proportions need for the desired R value.
More carbon produces less resistance, while more binder equals greater resistance. The resistor element is enclosed in a plastic case for insulation and mechanical strength. Joined to the two ends of the carbon resistance element are metal caps with leads of tinned copper wire for soldering the connections into a circuit. Carbon-composition resistors normally have a brown body and are cylindrical.
Carbon-composition resistors are commonly available in resistance values of 1Ω to 20MΩ. The power rating is generally 0.1, 0.125, 0.25, 0.5, 1, or 2W.

Carbon-film Resistors

Carbon film Resistor
A carbon-film resistor is a resistor in which a thin film of carbon is deposited onto an insulated substrate and then cut into a spiral body.
The resistance value of the resistor is controlled by varying the proportion of carbon to insulator. More carbon gives less resistance, while more insulating material gives greater resistance.
Compared to carbon-composition resistors, carbon-film resistors have the following advantages: lower and tighter tolerances, less sensitivity to temperature changes and aging, and less noise generated internally.

Metal-film Resistors

Metal-film resistors
A metal-film resistor is a resistor in which a thin film of metal is sprayed onto a ceramic substrate and then cut into a spiral body.
The length, thickness, and width of the metal spiral determine the exact resistance value.
Metal-film resistors offer more precise resistance values than the other type of film resistors, which are carbon-film resistors. Like carbon-film resistors, metal-film resistors are affected very little by temperature changes and aging. They also generate very little noise internally. 
Between the three types of resistors based on composition, carbon-composition resistors, carbon-film resistors, and metal-film resistors, in overall performance, metal-film resistors are the best, carbon-film the next best, and carbon-composition resistors last. 

Power Wirewound Resistors

Power Wirewound Resistors
Power wirewound resistors are resistors that can handle a large amount of power, usually up to 50 watts.
Typical resistors normally can handle between 0.25W to 2W of power. Power wirewound resistors can handle much, much more and are suitable for use in high-power applications.

Fusible Resistor

Cement Resistor
A Fusible Resistor is a wire-wound resistor that is designed to burn open easily when the power rating of the resistor is exceeded.
In this way, a fusible resistor serves dual functions. When the power isn't exceeded, it serves as a resistor limiting current. When the power rating is exceeded, it functions as a fuse, burning up, and becoming an open in the circuit to protect components in the circuit from excess current.

Variable Resistor
Types of Variable Resistor

Potentiometers

Potentiometer
A potentiometer is a 3-terminal variable resistor. By adjusting the wiper terminal, it can be used to represent a wide range of resistances in a circuit from anywhere near 0Ω to the specified resistance rating of the potentiometer. Therefore, for example, a 10KΩ potentiometer can be adjusted to give the resistance range from almost 0Ω to 10KΩ by adjusting the potentiometer knob.
Potentiometers are in wide use in circuits for a variety of uses, but their main fuction remains the same: to increase or decrease the amplitude of a signal in a circuit. When the resistance of the potentiometer is decreased, the amplitude of the signal increases. When the resistance is increased, the amplitude of the signal decreases. This can be used in circuits to control volume levels such as on speakers or for any adjustable controls.

Rheostats

Rheostat
A rheostat is a 2-terminal variable resistor.
As a variable resistor, it serves to vary the amount of voltage or current in a circuit.
Just like potentiometers, rheostats can be used to vary AC or DC signals. They differ from potentiometers in the fact that they only have two leads of which potentiometers have 3. However, the two still achieve the same function. While a potentiometer uses a third terminal to serve as the adjustable part, the rheostat uses a slider to vary resistance. If the slider isn't moved, the rheostat functions as a fixed resistor.
A rheostat is connected in a circuit by having the two leads connected in series with the load.

Thermistors

Thermistor
A thermistor is a thermally sensitive resistor whose resistance value changes with changes in operating temperature.
Because of the self-heating effect of current in a thermistor, the device changes resistance with changes in current.
Thermistors exhibit either a positive temperature coefficient (PTC) or a negative temperature coefficient (NTC). If a thermistor has a positive temperature coefficient, its resistance increases as the operating temperature increases. Conversely, if a thermistor has a negative temperature coefficient, its resistance decreases as the operating temperature increases.
How much the resistance changes with changes in the operating temperature depends on the size and construction of the thermistor. It's always best to check the datasheet of the thermistor in use to find out all the specifications of the thermistors.
Thermistors are frequently used in electronic circuits that handle temperature measurement, temperature control, and temperature compensation.

Photoresistors

Photoresistor
Photoresistors are resistors whose resistance values change according to the light striking the surface of the resistor. In a dark environment, the resistance of a photoresistor is very high, possibly several MΩ, depending on the resistance rating of the specific photoresistor in use. When intense light hits the surface, the resistance of the photoresistor drops dramatically, possibly to as low as 400Ω.
Thus, photoresistors are variable resistors whose resistance values change in regard to the amount of light hitting its surface.

The above list is an extensive list of the types of resistors which exist today. The last 4 resistors are variable resistors which change according to knob adjustments, heat, and light, respectively. 

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