**Definition of Resistance**

The property of the substance to resist the flow of electric current through it is known as resistance. The unit of resistance is Ohm. The conductors have free electrons moving randomly inside the metal, and on application of voltage, the electrons starts moving from the lower potential point to the higher potential point.

During drifting of the electrons, the collision between the electrons and atom and molecule of the conductor takes place, and this collision impede the path of flow of electrons. This impediment of flow of electron caused by collision of electrons with atom and molecule creates hinderance. The electrical hinderance in the path of current flow is the electrical resistance.

When we apply the voltage in a circuit, the current flow through the resistance. Let the voltage across resistance is V and current flowing in the circuit is I. The voltage across the resistance is proportional to the flow of electric current. According to Ohms’ Law ;

V ∝ I

V = RI

R = V/I Where,

V – Voltage

I – Current

R – **Resistance of the substance **

Hence, we can define the resistance as ratio of applied voltage to the current through the substance.

R = V/I

**Unit of Resistance**

On application of one volt of potential difference across the resistance cause 1 ampere current to flow through it, then the resistance is equal to 1 **Ω**. The **unit of resistance is volt per ampere o**r** ohm**, named after** George Ohm**. **The symbol of Ohm is omega (Ω ). **The** SI unit of the resistance** is Ohm(**Ω**)

R = V/I ( Ohm’s Law)

= 1 Volt/ 1 ampere

R =1 Ohm (Ω)

**Different Units of Resistance **

The larger units of resistance is **Kilo-Ohm, Mega-Ohm and Giga-Ohm.** The smaller units of resistance are **milli Ohm, Micro Ohm and nano Ohm.**

The relationship between different resistance units is as given below. The different units for resistance are;

Resistance unit | Value in Ohm(Ω) |

1 Giga Ohm (GΩ) | 10^{9 }Ω |

1 Mega Ohm (M Ω) | 10^{6 }Ω |

1 Kilo Ohm (K Ω ) | 10^{3 }Ω |

1 Milli Ohm (m Ω) | 10^{-3 }Ω |

1 Micro Ohm (μΩ ) | 10^{-6 }Ω |

1 Nano Ohm (nΩ ) | 10^{-9 }Ω |

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