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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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A large number of free electrons exist in ______.
Semiconductors
Metals
Insulators
Non-metals
Metals
Quick Summary: Metals have a large number of free electrons due to the overlapping of valence and conduction bands. These electrons are not bound to any specific atom and move freely throughout the crystal lattice, making metals excellent conductors of electricity.
Metals have a large number of free electrons due to the overlapping of valence and conduction bands. These electrons are not bound to any specific atom and move freely throughout the crystal lattice, making metals excellent conductors of electricity.
J=σE — Ohm's law in point form relating current density J, conductivity σ, and electric field E
I=nAevd — Current equation where n is free electron density, A is cross-section, and vd is drift velocity
In metals, the atomic orbitals of valence electrons overlap to form a continuous band structure called the conduction band. Because there is no energy gap (forbidden energy gap) between the valence band and the conduction band, thermal energy at room temperature is sufficient to excite electrons into the conduction band, facilitating high electrical conductivity.
Metals possess a high electron density (order of 10°28 electrons/m3)
The Fermi level in metals lies within the conduction band
Conductivity in metals decreases with an increase in temperature due to increased lattice scattering
Semiconductors have a forbidden energy gap, preventing free flow of electrons at absolute zero
High electrical and thermal conductivity
Good malleability and ductility for wiring
Susceptible to oxidation and corrosion
Conductivity decreases as temperature rises
Electrical transmission cables
Electronic circuit interconnects
Heat sinks for cooling components
In insulators, the forbidden energy gap is typically greater than 5 eV, preventing conduction.
In semiconductors, the energy gap is relatively small (e.g., ~1.1 eV for Silicon at 300K).
B is correct — Metals exhibit a large number of free electrons due to the absence of a band gap and the overlapping of conduction and valence bands.
Remember that while semiconductors become more conductive with heat, metals become less conductive due to increased electron-phonon scattering.