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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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In insulators the energy gap between valence and conduction bands is ______.
Very large
Zero
Very small
None of the above
Very large
Quick Summary: In insulators, the energy band gap between the valence band and the conduction band is very large, typically greater than 5 eV. This large gap prevents valence electrons from gaining sufficient thermal energy to jump into the conduction band, resulting in extremely high resistivity.
In insulators, the energy band gap between the valence band and the conduction band is very large, typically greater than 5 eV. This large gap prevents valence electrons from gaining sufficient thermal energy to jump into the conduction band, resulting in extremely high resistivity.
Eg=Ec−Ev>5 eV — Condition for electrical insulation
According to Band Theory, electrons reside in the valence band at absolute zero. In an insulator, the large forbidden energy gap (Eg>5 eV) acts as an insurmountable barrier for electrons at room temperature. Because they cannot transition to the conduction band, they are unable to move freely through the material to carry an electric current, hence the material acts as an electrical insulator.
The forbidden energy gap is the region where no electron states are permitted.
For insulators, Eg is typically larger than 5 electron-volts.
At room temperature, the number of free electrons in an insulator is negligible.
Materials like diamond (5.5 eV) and glass are classic examples of insulators.
High dielectric strength
Excellent electrical isolation capabilities
Cannot conduct electricity under normal conditions
Prone to dielectric breakdown if the electric field is extremely high
Dielectric materials in capacitors
Electrical cable insulation and coatings
Semiconductors have a moderate band gap (e.g., Silicon ~1.1 eV), allowing for control of conductivity.
Conductors have overlapping valence and conduction bands, meaning their band gap is zero.
A is correct — The forbidden energy gap in insulators is very large, preventing electron excitation to the conduction band.
Always remember the order: Insulators (Large Eg), Semiconductors (Small Eg), Conductors (Zero Eg or overlap).