Energy Bands & Band Gap Challenge
25 NEET-standard questions on classifying solids by resistivity and by energy bands: valence band, conduction band, the gap Eg, metals, insulators and semiconductors, the photon energy needed to cross the gap, and heating. Answer each one. If you get it wrong, Vidya Ma’am explains it with an animated movie you can control, a slider to play with, and a step-by-step solution. Then try again.
NCERT Physics XII Part II · Ch. 14 · pp. 324–327, 329 and 332Keys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
Classes by resistivityMetal 10⁻⁸–10⁻² · Semi 10⁻⁵–10⁶ · Insulator 10¹¹–10¹⁹ Ω mσ = 1/ρ; ranges are only indicative
BandsEg = Ec − Evvalence band below, conduction band above, gap between
The 3 eV ruleMetal: bands overlap or partly filled. Semiconductor: Eg < 3 eV. Insulator: Eg > 3 eV.Ge 0.7 · Si 1.1 · diamond 5.4 eV
Counting4N electrons, 8N statesat 0 K: valence band (4N) full, conduction band (4N) empty
Photon across the gapλmax = 1240 eV nm ÷ EgSi: 1127 nm · diamond: 230 nm
HeatingSemiconductor: more electrons cross, σ rises. Metal: more scattering, ρ rises.
Two carriersA crossing electron leaves a vacancy: electron + vacancy both conduct.
right first tryfixed after explanationstill to fix
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