# Electricity – Some Important Definition

#### Some Important Definitions

**Electricity **

A form of energy resulting from the existence of charged particles such as electrons or protons.

**Electric Charge **

Electric charge is a basic property of electrons, protons and other subatomic particles.

**Conductors **

Those substances through which electricity can flow are called conductors.

**Insulators **

Those substances through which electricity cannot flow are called insulators.

**Free Elecrons **

The presence of “free electrons” in a substance makes it a conductor (of electricity).

**Static Electricity **

In static electricity, the electric charges remain at rest (or stationary), they do not move.

**Current Electricity **

In current electricity, the electric charges are in motion (and produce an electric current)

**Electric Potential **

The electric potential (or potential) at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

**Potential Difference **

The potential difference between two points in an electric circuit is defined as the amount of work done in moving a unit charge from one point to the other point.

**Electric Current**

The electric current is a flow of electric charges (called electrons) in a conductor such as a metal wire.

**Electric Circuits **

A continuous conducting path consisting of wires and other resistances (like electric bulb, etc.) and a switch, between the two terminals of a cell or a battery along which an electric current flows, is called a circuit.

**OHM’s Law **

At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.

**Resistance **

The ratio of the potential difference applied between the ends of a conductor and the current flowing through it is a constant quantity called resistance.

**Good Conductors **

Those substances which have very low electrical resistance are called good conductors.

**Resistors **

Those substances which have comparatively high electrical resistance, are called resistors

**Superconductor **

A superconductor is any material that can conduct electricity with no resistance.

**Resistivity **

Resistivity of the material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross-section.

**Conductivity **

Conductivity defines a material’s ability to conduct electricity. Electric current can flow easily through a material with high conductivity.

**Semiconductor **

A material that is neither a good conductor of electricity nor a good insulator, but has properties of electrical conductivity somewhere between the two.

**Alloy **

An alloy is a substance made by melting two or more elements together, at least one of them metal.

**Alternating Current **

an electric current that reverses its direction many times a second at regular intervals, typically used in power supplies.

**Direct Current **

Direct current is the unidirectional flow of an electric charge.

**Electric Power **

Electric power is the electrical work done per unit time.

**Heating Effect Of Current **

When an electric current is passed through a high resistance wire, like nichrome wire, the resistance wire becomes very hot and produces heat. This is called the heating effect of current.

#### Some Important Definitions of Units

**1 Coulomb **

One coulomb is that quantity of electric charge which exerts a force of 9 x 109 newtons on an equal charge placed at a distance of 1 metre from it.

**1 Volt **

The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving I coulomb of electric charge from one point to the other.

**1 Ampere **

When I coulomb of charge flows through any cross-section of a conductor in 1 second, the electric current flowing through it is said to be 1 ampere.

**1 ohm **

1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of 1 ampere flows through it.

**Resistivity **

The resistivity of a substance is numerically equal to the resistance of a rod of that substance which is 1 metre long and 1 square metre in cross-section.

**1 Watt **

The power of 1 watt is a rate of working of 1 joule per second.

**1 KWh **

One kilowatt-hour is the amount of electrical energy consumed when an electrical appliance having a power rating of 1 kilowatt is used for I hour.