Misconceptions — Semiconductors & Logic Gates — Notes | NoteTube

#	Misconception	Why It Seems Right	The Truth	NEET Implication
1	"n-type semiconductor is negatively charged"	Majority carriers are electrons (negative charges)	Neutral: each dopant atom donates 1 electron AND contributes 1 extra nuclear proton; charges balance	Direct NEET trap question: choose "electrically neutral"
2	"p-type semiconductor is positively charged"	Holes are positive carriers	Neutral: trivalent dopant has fewer protons AND fewer electrons; still charge-balanced	Same as above — both n and p are neutral
3	"Semiconductor conductivity decreases with temperature (like metals)"	Increased vibrations = more resistance	Semiconductor conductivity INCREASES with T — more electrons thermally excited across E_g	Temperature coefficient MCQs test exactly this reversal
4	"Zener diode works in forward bias"	"All diodes work in forward bias for current"	Zener's UNIQUE feature is stable reverse breakdown voltage V_Z — this is the entire point	"In which bias does Zener operate for regulation?" → reverse bias
5	"Photodiode must be in forward bias to detect light"	Needs current to flow → forward bias	Reverse bias gives faster response, lower dark current, better linearity for detection	Application MCQs: photodiode operates in REVERSE bias
6	"Solar cell needs external power supply"	Most diodes need bias to function	Solar cell generates its OWN EMF via photovoltaic effect — no external bias needed	This distinguishes solar cell from photodiode
7	"NAND gate is universal but NOR is not (or vice versa)"	NAND is more commonly discussed	BOTH NAND and NOR are independently universal	"Which gates are universal?" → select BOTH NAND and NOR
8	"Full-wave rectifier output frequency = input frequency"	Still the same 50 Hz signal being rectified	Both half-cycles are used: f_out = 2 × f_in = 100 Hz for 50 Hz input	Direct numerical: "output frequency of full-wave rectifier = ?"
9	"De Morgan: $\overline{A+B} = \overline{A} + \overline{B}$ "	Intuitive to just add bars separately	$\overline{A+B} = \overline{A} \cdot \overline{B}$ — the operator FLIPS from + to ·	Boolean simplification questions test this exact rule
10	"Si and Ge have similar barrier potentials"	Both are semiconductors with similar properties	Si ≈ 0.7 V; Ge ≈ 0.3 V — notably different	"Which has higher knee voltage?" → Si (0.7 V vs 0.3 V)