# Physics - Electricity

## Introduction

• If the electric charge flows through a conductor, such as a metallic wire, it is known as the electric current in the conductor.

• A continuous and closed path of an electric current is known as an electric circuit (as shown in the image given below) −

• In an electric circuit, usually, the direction of electric current (known as positive charges), is considered as opposite to the direction of the flow of electrons, which are considered as negative charges.

• The SI unit of electric charge is coulomb (C).

• Coulomb is equivalent to the charge contained in closely 6 × 1018 electrons.

• The electric current is expressed by a unit known as an ampere (A).

• It was named after the French scientist Andre-Marie Ampere.

• One ampere constitutes by the flow of one coulomb of charge per second, i.e., 1 A = 1 C/1 s.

• The instrument that measures electric current in a circuit is known as ammeter.

• The electric current flows in the circuit starting from the positive terminal to the negative terminal of the cell through the bulb and ammeter.

## Electric Potential and Potential Difference

• The electrons of a conductor move only if there is a difference of electric pressure, known as the potential difference.

• The chemical action within a cell produces the potential difference across the terminals of the cell. Further, when this cell is linked to a conducting circuit element, the potential difference sets the charges in motion (in the conductor) and generates an electric current.

• Alessandro Volta (1745–1827), an Italian physicist, first noticed the electric potential difference; therefore, the SI unit of electric potential difference is given volt (V).

• The instrument that measures the potential difference is known as the voltmeter.

## Circuit Diagram

• Some defined symbols are used to illustrate the most commonly used electrical components in circuit diagrams.

• The following table describes some of the symbols commonly used to define the electric components −

Components Symbols
An electric cell
A battery or combination of cells
Plug key or switch (Open)
Plug key or switch (closed)
A wire joint
Wires crossing without joining
Electric bulb
A resistor of resistance R
Variable resistance or rheostat
Ammeter
Voltmeter

## Ohm’s Law

• A German physicist, Georg Simon Ohm in 1827, stated that “The electric current flowing through a metallic wire is directly proportional to the potential difference (V), across its ends provided its temperature remains the same.”

## Electric Power

• The rate at which electric energy is dissipated or consumed in an electric circuit is known as electric power.

• The SI unit of electric power is watt (W).