Conductivity and resistivity — lesson. Science State Board, Class 7.

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Resistance:

An electrical component that resists or hinders the flow of electric charges in a circuit is called resistance. The SI unit of resistance is $ohm$ ($Ω$).

The higher the resistance in a circuit, the higher the potential difference needed to move an electric charge through the circuit. We can express resistance as a ratio. Resistance of a component is the ratio of the potential difference across it to the current flowing through it.

Resistance can be mathematically expressed as,

R = \frac{V}{I}

where,

$R$ $-$ Resistance

$V$ $-$ Voltage

$I$ $-$ Current

Electrical conductivity ($σ$):

Specific conductance or Electrical conductivity is the measure of a material's ability to conduct an electric current. It is commonly represented by the Greek letter $σ$ ($sigma$). The SI Unit of electrical conductivity is $Siemens/meter$ ($S/m$).

Electrical resistivity ($ρ$):

Electrical resistivity is the property of a material that quantifies how strongly that material opposes or hinders electric current flow. The SI unit of electrical resistivity is the ohm-metre ($Ωm$). It is also called specific electrical resistance or volume resistivity.

Material	Electrical conductivity ($σ$)	Electrical resistivity ($ρ$)
Silver	$1.59 \times 10^{- 8}$	$6.3 \times 10^{7}$
Copper	$1.68 \times 10^{- 8}$	$5. 98 \times 10^{7}$
Annealed copper	$1.72 \times 10^{- 8}$	$5.8 \times 10^{7}$
Aluminium	$2.82 \times 10^{- 8}$	$3.5 \times 10^{7}$

Similarities of electric current with water flow:

An electric current is the flow of electrons through a conductor (like a copper wire). We can't see electrons. However, we can imagine the flow of electric current in a wire-like water flow in a pipe. Let us know the analogy of the flow of electric current with the water flow. Water flowing through pipes is similar to an electrical circuit. Water flow in the tube because the pump pushes the water.

Electric current	Water flow
Flow of electrons in a conductor	Flow of water in a pipe
The pressure or potential difference is generated by the battery, which drives electrons through the electric circuit.	The pressure generated by the pump drives water through the pipe.
The electric circuit's resistance resists the flow of electrons and creates a voltage drop from one end to the other.	Any dust or rust present in the pipe may slow the flow of water and creates a pressure difference from one end to the other end of the pipe, like resistance in an electric circuit.

Current and water analogy

Reference:

https://commons.wikimedia.org/wiki/File:Silverchain.jpg

https://pixabay.com/photos/copper-metal-copper-wire-industry-5547397/

https://pixabay.com/photos/steel-tube-square-steel-tube-5528518/

https://commons.wikimedia.org/wiki/File:Water_pump_flow.jpg

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Material	Electrical conductivity (\(σ\))	Electrical resistivity (\(ρ\))
Silver	\(\) $1.59 \times 10^{- 8}$ \(\)	\(\) $6.3 \times 10^{7}$ \(\)
Copper	\(\) $1.68 \times 10^{- 8}$ \(\)	\(\) $5. 98 \times 10^{7}$ \(\)
Annealed copper	\(\) $1.72 \times 10^{- 8}$ \(\)	\(\) $5.8 \times 10^{7}$ \(\)
Aluminium	\(\) $2.82 \times 10^{- 8}$ \(\)	\(\) $3.5 \times 10^{7}$ \(\)

5. Conductivity and resistivity

Theory: