### Inductors

Inductors store energy in a magnetic field. The magnetic field is created by passing current through a coil of wire, as is done in an electromagnet such as those used to lift scrap iron.
In electric circuits inductors often play the role of smoothing devices that reduces current variations.But when the current is forced to change abruptly, the inductor generates a large induced voltage- - large enough to cause a spark in the extreme case of an automobile ignition circuit.
This two terminal device consists of a wire coil wound around a core.The core may be cylindrical or it may be doughnut-shaped. The coil has N turns , insulated from one another and from the core.When the wire carries the current i, a magnetic field is created in the space around the coil and becomes concentrated within the core.Like an electric field, the magnetic field holds energy that comes from the source that established the field.hence,

An inductor stores energy in a magnetic field produced by current through a wire coil.The strength of the field expressed in terms of magnetic flux through the core.The proportionality constant L is the inductance which is measured in henrys (H).

### CAPACITORS

Capacitors store energy in an electric field. The electric field is created by displacing positive and negative charges such that they tend to attract each other.

In electric circuits, capacitors are used to store energy for flash lamps, to provide a tuning mechanism for radios, and to perform various other useful tasks.

This device consists of two metallic surfaces or plates separated by a dielectric.Ideally , the perfect dielectric is insulator,so that it prevents charge flow inside the capacitor.

When a voltage source is attached to a capacitor an electric field is created between the plates. This field holds the energy supplied by the source to move the charges.so

A capacitor stores energy in an electric field produced by displaced charge on the plates.Mathematically,

q= C v where the proportionality constant C is called the capacitance,defined as

C= q/v

Capacitance is measured in farads(F),named in the honour of English experimentalist Michael Faraday(1791-1867).

TYPES OF CAPACITORS:
Capacitors come in a wide variety of shapes and sizes.Particular families are categorized according to the type of dielectric material.some capacitors often consist of thin ceramic disks with metal coatings on the plat surfaces to from the plates.
Larger capacitances are achieved by rolling sheets of metal foil and flexible dielectric into a tubular shape.The dielectric is usually a plastic film such as mylar.

For,
Air variable capacitor's capacitance is 10-500 pF, voltage is 500 and RC is Infinity.
Ceramic disk capacitor's capacitance is 5 pF-50 nF, voltage is 600-1000 and RC is 1000.
Plastic film capacitor's capacitance is 1 nF-5 uF, voltage is 100-600 and RC is 100,00.
Electrolytic capacitor's capacitance is 1 uF-1 F, voltage is 6-250 and RC is 50-500.

### Full Wave Rectification

A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient.

Full wave rectification:

The positive half cycle:

During the positive half cycle of the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current flows through the load as shown below

The negative half cycle:

During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch of as they are now reverse biased. The current flowing through the load is the same direction as before.

Full wave rectification for smoothing DC:

With the full wave rectification we get the pulsating DC with the ripples.For smooth DC we use capacitors to remove ripples.

### Half Wave Rectification

In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output.Half wave rectification can be achieved with a single diode in a one phase supply, or with three diodes in a three-phase supply.

During the first half cycle of the waveform the diode is forward biased and current flows around the circuit formed by the diode, the transformer winding and the load.
During the second half cyclethe diode is reverse biased and no current flows.
The diode only conducts on every other half cycle. Hence, HALF-WAVE RECTIFICATION.
The rectified voltage is DC (it is always positive in value). However, it is not a steady DC but PULSATING DC. It needs to be smoothed before it becomes useful.

### Rectifier & Inverter

The Electric device which converts the alternating current AC to direct current DC is called rectifier. And this process is known as rectification.
Rectifiers are used in the detection of signals and in power supplies.

&

The electric device which converts the direct current DC to alternating current AC is called Invertor. Read More!

### SemiConductors

A semiconductor is a solid material that has electrical conductivity in between a conductor and an insulator; it can vary over that wide range either permanently or dynamically.

Semiconductors are important in electronic technology. Semiconductor devices, electronic components made of semiconductor materials, are essential in modern consumer electronics, including computers, mobile phones, and digital audio players. Silicon is used to create most semiconductors commercially, but dozens of other materials are used Read More!

### Conductors & Insulators

CONDUCTORS:
In science and engineering , a conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminium, the movable charged particles are electrons.

Positive charges may also be mobile in the form of atoms in a lattice missing electrons (called "holes") or ions, such as in the electrolyte of a battery.

INSULATORS:
Insulator is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves. Read More!

### Atomic Structure

An atom is the smallest particle of an element that retains the characteristics of that element.Each of the known 109 elements has atoms that are different from the atoms of all other elements.

According to the Bohr model, atoms have a planetary type of structure that consists of central

nucleus
surrounded by orbiting electrons .The nucleus consists of positively charged particles called protons and uncharged particles called neutrons .The basic particles of negative charge are called electrons.

A look of helium atom is:

### Kirchhoff's Voltage Law

What is loop?
A loop is any path that goes from node to node and returns to the starting node, passing only once through each node.

Kirchhoff's Voltage Law:

The sum of the voltage drops around any loop equals the sum of the voltage rises.

or

The algebraic sum of all voltage drops around any loop equals zero.

Mathematically,

v1 + v2 + v3 + v4 = 0
or

$\sum_{k=1}^n V_k = 0$

Parallel Connection:
Two or more elements are in parallel when their terminals are connected to the same pair of nodes.

Also that elements in parallel have the same voltage across each one of them.

### Kirchhoff's Current Law

what is node?

A node is any connection point of two or more circuit elements.

Kirchoff's current law:

The sum of the currents leaving any node equals the sum of the currents entering that node.

or

The algebraic sum of all currents into any node equals zero.

mathematically,

i1 + i4 = i2 + i3

or
$\sum_{k=1}^n I_k = 0$

Series Connection:
Two or more elements are in series when each node connects just two elements.

Also that elements in series carry the same current.

### LED Flasher Circuit Using 555 Timer IC

This is a simple LED flasher project that uses a common 555 timer IC for its operation. It is configured as an astable mode which means that its output is a square wave oscillator. Two LEDs are connected to its output in such a way that when one LED is ON, the other LED will turn OFF. It uses only 10 simple parts that are easily available at any electronic shops.
Capacitor C2 charges exponentially through resistors R1, R2 and the resistance of the trimpot. When C2 has charged to about 2/3 VCC it stops charging and it discharges to about 1/3 VCC through R2 and the trimpot resistance via pin 7. This is the standard operation of a 555 timer. When a Vcc of 5 V to 15 V DC is applied to the circuit, the LED will start to flash. The frequency of the flashing can be changed by varying the resistance of the potentiometer or trimpot.

Parts List
The parts list of the simple LED project is as shown below.

### The 555 Timer IC

The 555 Timer is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. The IC was designed and invented by Hans R. Camenzind. It was designed in 1970 and introduced in 1971 by Signetics (later acquired by Philips). The original name was the SE555/NE555 and was called "The IC Time Machine".

The 555 gets its name from the three 5-k Ohm resistors used in typical early implementations. It is still in wide use, thanks to its ease of use, low price and good stability. As of 2003[update], 1 billion units are manufactured every year.

The 555 timer is one of the most popular and versatile integrated circuits ever produced. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8).

The 555 has three operating modes:

* Monostable mode: in this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bouncefree switches, touch switches, Frequency Divider,Capacitance Measurement, Pulse Width Modulation (PWM) etc

* Astable - Free Running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.

* Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bouncefree latched switches, etc.

The connection of the pins is as follows:

Nr. Name Purpose

1 GND Ground, low level (0V)
2 TR A short pulse high → low on the trigger starts the timer
3 Q During a timing interval, the output stays at +VCC
4 R A timing interval can be interrupted by applying a reset pulse to low (0V)
5 CV Control voltage allows access to the internal voltage divider (2/3 VCC)
6 THR The threshold at which the interval ends (it ends if U.thr → 2/3 VCC)
7 DIS Connected to a capacitor whose discharge time will influence the timing interval
8 V+, VCC The positive supply voltage which must be between 3 and 15 V

In the astable mode, the high time from each pulse is given by

high = 0.693.(R1 + R2).C

and the low time from each pulse is given by

low = 0.693.R2.C

where R1 and R2 are the values of the resistors in ohms and C is the value of the capacitor in farads.

Specifications

These specifications apply to the NE555. Other 555 timers can have better specifications depending on the grade (military, medical, etc).

* Supply voltage (VCC) 4.5 to 15 V
* Supply current (VCC = +5 V) 3 to 6 mA
* Supply current (VCC = +15 V) 10 to 15 mA
* Output current (maximum) 200 mA
* Power dissipation 600 mW
* Operating temperature 0 to 70 °C Read More!

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