Trap 1 — Semiconductor charge: n-type is NOT negatively charged; p-type is NOT positively charged. BOTH are electrically neutral because dopant atoms bring equal proton and electron counts into the crystal lattice. Choosing "electrically neutral" is always correct.

Trap 2 — Zener bias: Zener diode for voltage regulation MUST be in reverse bias. Forward-biased Zener behaves like an ordinary diode — this is NOT its application. "Zener → Reverse bias → Regulation" is the complete rule.

Trap 3 — Photodiode bias: Photodiode operates in reverse bias for detection (wider depletion region → better sensitivity and faster response). Forward-biased photodiodes exist but are NOT the standard detection mode in NEET syllabus.

Trap 4 — Rectifier frequency: Half-wave rectifier: f_out = f_in (50 Hz in = 50 Hz out). Full-wave rectifier: f_out = 2 × f_in (50 Hz in = 100 Hz out). The "2×" applies ONLY to full-wave; many students apply it to both.

Trap 5 — Universal gates: Both NAND and NOR are universal gates. Questions often offer options like "only NAND" or "only NOR" — the correct answer requires selecting BOTH.

Trap 6 — Temperature coefficient: Semiconductor conductivity INCREASES with temperature (negative coefficient). Metal conductivity DECREASES. NTC thermistors exploit this semiconductor property.

Trap 7 — De Morgan's operator flip: $\overline{A+B} = \overline{A} \cdot \overline{B}$ (+ becomes ·, NOT +). Students who write $\overline{A} + \overline{B}$ apply it incorrectly. The operator always FLIPS.

Trap 8 — NOR vs AND confusion: NOR output is 1 only when ALL inputs are 0 (not when inputs are equal, not when both are 1). AND output is 1 only when ALL inputs are 1. These are opposite extremes.

Trap 9 — Si vs Ge values: Si has higher barrier potential (0.7 V) AND higher band gap (1.1 eV). Ge has lower values (0.3 V, 0.67 eV). Never swap these pairs.

Trap 10 — Solar cell needs no bias: Unlike photodiodes (reverse bias), solar cells operate with NO external power supply. The photovoltaic effect generates the EMF internally.