Unit of Resistance

What is the Unit of Resistance?

SI unit of resistance in physics or unit of resistance in physics:

The ohm, which is defined as a volt per ampere, is the si unit of resistance. In honour of German physicist George Simon Ohm, the name has been preserved. The unit is sometimes written as a word or represented by the Greek letter omega in uppercase.

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Specific Resistance (Resistivity)

The resistance $R$ of a conductor depends upon its length $L$, cross-sectional area $A$, and the nature of the material. For a conductor of uniform cross-section:

Resistance is directly proportional to its length

$
R \propto L
$

Resistance is inversely proportional to its cross-sectional area

$
R \propto \frac{1}{A}
$

Combining these relations,

$
\begin{aligned}
& R \propto \frac{L}{A} \\
& R=\rho \frac{L}{A}
\end{aligned}
$

where $\rho$ (rho) is a constant of proportionality called specific resistance or resistivity of the material.
Specific resistance is defined as the resistance of a conductor having unit length and unit cross-sectional area.

$
\rho=\frac{R A}{L}
$

The SI unit of resistivity is ohm metre ( $\Omega \mathrm{m}$ ).

Ohm's Law

Ohm's law states that, at constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.

$
\begin{gathered}
I \propto V \\
V=I R
\end{gathered}
$

or

$
R=\frac{V}{I}
$

where $V$ is the potential difference, $I$ is the current, and $R$ is the resistance of the conductor. The resistance depends upon the material, dimensions, and physical condition of the conductor.

Si Unit of Resistance-

The si unit of resistance is the ohm (Ω).

International ohm unit definition-

1 Ohm is the resistance of a mercury column with a temperature of melting ice, a uniform cross-sectional area, a length of 106.3 cm, and a mass of 14.4521 g.

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Popular Resistance Units

Electrical resistance is a fundamental concept in physics and electronics. It measures how much a material or component opposes the flow of electric current. Resistance is represented by the symbol $\mathbf{R}$ and is measured in different units depending on the scale of measurement.
1. Ohm ( $\boldsymbol{\Omega}$ ) - SI Unit

The most commonly used unit of resistance is the ohm ( $\boldsymbol{\Omega}$ ).
One ohm is defined as the resistance between two points of a conductor when a potential difference of 1 volt produces a current of 1 ampere.

$1 \Omega=\frac{1 V}{1 A}$

2. Milliohm ( $\mathbf{m} \boldsymbol{\Omega}$ )

• $1 \mathrm{~m} \Omega=10^{-3} \Omega$
• Used for measuring very small resistances.

3. Kiloohm ( $\mathbf{k} \boldsymbol{\Omega}$ )

• $1 \mathrm{k} \Omega=10^3 \Omega$
• Common in electronic circuits.

4. Megaohm ( $\mathrm{M} \Omega$ )

• $1 \mathrm{M} \Omega=10^6 \Omega$
• Used for high resistance values.

5. Microohm ( $\boldsymbol{\mu} \boldsymbol{\Omega}$ )

• $1 \mu \Omega=10^{-6} \Omega$
• Used in precision electrical measurements.

Some important points-

• Temperature-dependent resistance. If there is a consistent holding of other physical amounts, resistance increases with increasing metal temperature. The resistivity decreases significantly for glass, however, at very high temperatures.
• In the superconducting state, superconductors have zero resistance (at very low temperatures).
• The resistance of semiconductors decreases as the temperature increases.

Also check-

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NCERT Physics Notes:

• NCERT Notes Class 11th Physics
• NCERT Notes Class 12th Physics
• NCERT Notes For All Subjects