Important Terminology Related to Electricity

Current (I)

An electric current is the flow of electrons through a conductor. The rate of flow of charge is called current means the charge passes through a conductor in unit time. If charge Q is flowing through a cross-section of a conductor in time t then the

Current (I)  =\frac{Q}{T} 

The SI unit of charge is Coulomb (C). Current is expressed in Ampere (A). The charge of one electron is

1.6\times10^{-19}C

Ampere: One-ampere current is said to flow in a conductor if one Coulomb charge flows
through it every second.

1A=\frac{1C}{1s} 

Electrons move from the negative end to the positive end, conventionally, the direction of current flow is taken to be opposite of the direction of flow of electrons from the+ve end to the –ve end of a cell.

A potential difference of a cell (Volt -V)

The Potential difference between the positive and negative terminals of a cell is the potential difference of that cell. Potential difference creates a force on electrons to move from height potential to lower potential and results in the flow of electricity through a conducting wire connected to the two ends of the cell. The amount of work done to carry a unit positive charge from point A to point B is
called the electric potential difference between the two points

Voltage=\frac{Work}{Charge}\\
1V=\frac{1J}{1C}

The unit of potential difference in the SI system is the volt

Classification of voltage

• Low voltage – 0 to 250 Volt
• Medium voltage – 250 to 650 volt
• High voltage – 650 to 11000 volt
• Extra high voltage – above 11000 volt

Resistance (R)

Oppose to the flow of current is called resistance. At a given temperature, the resistance
(R) of a conductor depends on its length (L), area of cross-section (A), and the material it is made of.

R= ρ \frac{L}{A}

ρ is the constant of proportionality and is called the resistivity of the material. The SI unit is an Ohm meter (Ωm). Resistivity is a specific property of a material and different materials have different resistivity.

EMF (Electro Motive Force )

Due to EMF electrons move from one place to another place. The SI unit is Volt

Load (Rl)

The sum of all connected instruments on an electrical circuit is called the electrical load. Ex Fan, TV, AC, etc.

Terminal voltage

The potential difference between the two terminals of the generator, motor, or any electrical appliance is called terminal voltage. The value of terminal voltage is always less than the EMF value.

Vt=E- IR