1
Question
State the order of resistivity of (i) a metal, (ii) a semiconductor and (iii) an insulator.
State the order of resistivity of (i) a metal, (ii) a semiconductor and (iii) an insulator.
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Solution
The correct option is C insulator > semiconductor > metal
Resitivity is a measure of the resistance to electrical conduction for a given size of material.
Metals are good electrical conductors with high conductivity and low resistivity, while non-metals are mostly poor conductors with low conductivity and high resistivity.
In metals, the Fermi level lies in the conduction band giving rise to free conduction electrons. However, in semiconductors the position of the Fermi level is within the band gap, approximately half-way between the conduction band minimum and valence band maximum for intrinsic (undoped) semiconductors. This means that at 0 kelvin, there are no free conduction electrons and the resistance is infinite. However, the resistance will continue to decrease as the charge carrier density in the conduction band increases. In extrinsic (doped) semiconductors, dopant atoms increase the majority charge carrier concentration by donating electrons to the conduction band or accepting holes in the valence band. For both types of donor or acceptor atoms, increasing the dopant density leads to a reduction in the resistance, hence highly doped semiconductors behave metallically.
An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.
Hence the order of resistivity is insulators with highest resistivity, semiconductors in between and conductors with least resistivity.
Resitivity is a measure of the resistance to electrical conduction for a given size of material.
Metals are good electrical conductors with high conductivity and low resistivity, while non-metals are mostly poor conductors with low conductivity and high resistivity.
In metals, the Fermi level lies in the conduction band giving rise to free conduction electrons. However, in semiconductors the position of the Fermi level is within the band gap, approximately half-way between the conduction band minimum and valence band maximum for intrinsic (undoped) semiconductors. This means that at 0 kelvin, there are no free conduction electrons and the resistance is infinite. However, the resistance will continue to decrease as the charge carrier density in the conduction band increases. In extrinsic (doped) semiconductors, dopant atoms increase the majority charge carrier concentration by donating electrons to the conduction band or accepting holes in the valence band. For both types of donor or acceptor atoms, increasing the dopant density leads to a reduction in the resistance, hence highly doped semiconductors behave metallically.
An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.
Hence the order of resistivity is insulators with highest resistivity, semiconductors in between and conductors with least resistivity.
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