LED is a digital display used in calculators, watches etc. LED stands for:

Question

UnlockIAS · Accepted Answer

Correct — C, Light Emitting Diode. An LED is a semiconductor p–n junction diode that gives out light when it is forward biased: electrons crossing the junction recombine with holes and release the energy as photons, a process called electroluminescence. The colour depends on the band gap of the semiconductor used. The seven-segment displays in calculators and digital watches are simply small LEDs arranged in a figure-of-eight pattern, which is why the question ties the acronym to those devices.

Why the other options are wrong — (a) The first half is right but the 'D' is Diode, not Display. The LED is the individual light-emitting component; a display is what you build by arranging many of them (as in a seven-segment or LED panel display).  (b) This mixes LED up with LCD — Liquid Crystal Display. An LCD contains liquid crystals that only block or pass light and therefore needs a backlight or ambient light; an LED generates its own light. Note also that 'Liquid Electronic' is not the expansion of LCD either.  (d) No such device exists. There is nothing liquid in an LED — it is a solid-state semiconductor component made from doped crystals such as gallium arsenide or indium gallium nitride.

Concept: A diode is a p–n junction that conducts in one direction only. In an LED the semiconductor is chosen so that the energy released when electrons and holes recombine comes out as visible (or infrared) light rather than only heat — electroluminescence. Because the photon energy equals the band gap, the material fixes the colour: gallium arsenide gives infrared/red, gallium phosphide green, indium gallium nitride blue. Combining a blue LED with a yellow phosphor is how white LED lamps are made.

State PCS 2026 Q33 — Science & Technology PYQ with Answer

State PCS 2026 Q33 — Science & Technology PYQ with Answer