Capacitor

                                 A capacitor is a two-terminal passive device.Capacitor stores electrical energy in the form of electric charges. First capacitors are called as electric condenser. These capacitor consists of two parallel plates in which positive and negative charges stores. In between the two plates there will be a dielectric material like paper, ceramic and mica. When the electric energy is applicable capacitor get charged stores energy and power is switched off then the capacitor gets discharged. The amount of charges can be stored is given by capacitance. It is measured in the unit Farad. There are various types in capacitor. They are:

• Fixed capacitor
• Variable capacitor
• Polarized capacitor

Capacitor experiment explained in the below video:

Modulation | Why it is necessary..?

Modulation

                  Modulation is a process of changing one or more properties in a transmitting signal (message signal) by adding noise signal (carrier signal) to it. If we transmit a signal without modulation, we can't send the signal to a long distance, for covering the more distance we must modulate the message signal before transmitting. By using the modulation technique we can secure the message,what we transmit.

Example : 

                If we throw a sheet of paper, it will not reach a long distance. If we want the paper to reach a long distance, then we can add some noise(unwanted) to the paper that is crushing the paper or throwing the paper with a stone in it. Now the paper reaches a long distance.

Why modulation is necessary..?

Demodulation

                    Demodulation is a process of removing the carrier signal what we have added in modulation.This is the process of recovering the original message signal.

                    By removing the stone in the crushed paper is the example of recovering the original signal, ie,) demodulation.

Conductors and Insulators

Conductors

                   In conductors, electric current can flow freely. Metals are mostly conductors. Metals such as Gold, silver, copper are conductors. And all the non-metal are not non conductors. Some non- metals like graphite and the human body are also good conductor. They have very low resistance and high conductance. The resistivity of a conductor will never be ZERO(except only one metal). The outermost electron in a conductor is loosely bounded. so, It can be easily moved throughout the material(conductor) by giving current to it.

Resistivity of conductors :

Gold                - 2.44 x 10 ⁻⁸ ohm m
Silver              - 1.59 x 10 ^-8 ohm m
Copper            - 1.7 x 10 ^-8 ohm m
Aluminum - 2.65 x 10 ^-8 ohm m

A video explaining Conductor & Insulator in தமிழ்

Insulators

                In insulators, electric current can't flow freely. Non-metals are mostly insulators. Non-metals such as glass , mica are insulators.They have extremely high resistance and very low or nil in conductance.The outermost electrons in the insulators are tightly bounded. so, It can't be easily moved throughout the material(insulator) by giving current to it.

Resistivity of inductors :

Glass    - 10 ¹² ohm m

Mica     - 9 x 10 ¹³ ohm m

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