Special-purpose Diodes Challenge
25 NEET-standard questions on the Zener diode and voltage regulator, the LED, the photodiode and the solar cell. 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.
NEET UG 2026 syllabus · not in the 2026-27 NCERT textKeys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
ZenerHeavily doped, used in reverse bias at breakdown. V across it ≈ VZ.Zener in parallel with the load, resistor in series
Regulator currentsIR = IZ + ILIR = (Vin − VZ)/Rs · IL = VZ/RL
Check firstIf the voltage without the Zener is below VZ, the Zener is off.
LEDForward bias · recombination · photon out · hν ≈ EgGaAs: infrared · GaP: red/green
Colourλ(nm) = 1240 / Eg(eV)bigger gap = shorter wavelength
PhotodiodeReverse bias · needs hν ≥ Eg · Iph ∝ intensityI–V in the third quadrant
Solar cellNo external bias · photovoltaic effect · I–V in the fourth quadrantVoc ≈ 0.5–0.7 V · Pmax = FF·Voc·Isc
right first tryfixed after explanationstill to fix
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