Valves to Solid-State Challenge
25 NEET-standard questions on vacuum tubes versus solid-state devices, and on classifying metals, semiconductors and insulators by resistivity. 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. 323–324Keys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
“Valve = one-way”Vacuum tube: electrons from a heated cathode flow only to the plate, in vacuum, at about 100 V.Solid state: small, low power, low voltage, long life, carriers inside the solid.
Electrodesdiode 2 · triode 3 · tetrode 4 · pentode 5Triode = cathode + plate + grid
Resistivity rangesmetal 10⁻² to 10⁻⁸ · semi 10⁻⁵ to 10⁶ · insulator 10¹¹ to 10¹⁹ Ω mIndicative only, and not the only criterion
Conductivityσ = 1/ρMetal 10²–10⁸ · semi 10⁵–10⁻⁶ · insulator 10⁻¹¹–10⁻¹⁹ S m⁻¹
Resistance of a barR = ρL/AConvert cm and mm² to metres first: 1 mm² = 10⁻⁶ m²
Elemental vs compoundElemental: Si, Ge. Inorganic compound: CdS, GaAs, CdSe, InP.Organic: anthracene, phthalocyanines. Polymers: polypyrrole, polyaniline, polythiophene
Timeline1930s idea · 1948 transistor · after 1990 organic devicesMost devices today use Si, Ge and inorganic compounds
right first tryfixed after explanationstill to fix
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