Draw the I-V characteristic curves of a light emitting diode (LED) for yellow and green light. On what factors

Question 61 of 64

Q. Draw the I-V characteristic curves of a light emitting diode (LED) for yellow and green light. On what factors do the wavelength and intensity of the light emitted by an LED depend?

West Bengal WbchseWest Bengal HS (WBCHSE) Board 2026Subjective· 3mImportance★★★★★

95% · 61/64 Questions

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Forward I-V characteristics of yellow and green LEDs: both rise sharply after a knee voltage, with the green (larger band gap) turning on at a higher voltage.

Both LED I-V characteristics stay flat until a knee voltage and then rise sharply in forward bias, with the green LED's knee at a higher voltage than the yellow LED's; the emitted wavelength is set by the band gap (lambda = hc/Eg) and the intensity by the forward current.

Description of the I-V characteristic curves (current on y-axis, forward voltage on x-axis):

In forward bias the current is negligible until the applied voltage reaches a threshold (knee/turn-on) voltage, after which the current rises steeply and almost linearly.
The knee voltage of an LED is roughly equal to Eg/e. Green light has a shorter wavelength (higher photon energy) than yellow, so a green LED needs a larger band gap and therefore turns on at a HIGHER forward voltage. Plotted together, the two curves have the same general shape but the green curve is shifted to the right of the yellow curve (larger knee voltage).
(In reverse bias an LED passes only a tiny current and has a low reverse breakdown voltage, so it is normally operated in forward bias.)

Factors: …

Start your 14-day free trial to unlock the full solution →

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2023Set ANNUAL1 mark
$Q. Light emitting diodes emit light in which bias? OR Write the Boolean expression for NOR gate.$
›Reveal solutionSolution

An LED is a forward-biased p-n junction diode; light is emitted only when the junction is forward biased, allowing electron-hole recombination that releases energy as photons.

A light emitting diode (LED) is a heavily doped p-n junction that emits light through spontaneous emission when charge carriers recombine. This recombination only happens efficiently when the diode is forward biased — the p-side connected to the positive terminal and n-side to the negative terminal of the source. Forward bias injects majority carriers (el …

Start your 14-day free trial to see the full solution →
CBSE 2022Set ANNUAL1 markMCQ
$Q. The wavelength and intensity of light emitted by a LED depend upon$
(a) forward bias and energy gap of the semiconductor
(b) energy gap of the semiconductor and reverse bias
(c) energy gap only
(d) forward bias only OR Two photodiodes D1 and D2 are made of semiconductors having band gaps of 2.0 eV and 2.2 eV respectively. The diode which will be able to detect light of wavelength 6200 Å is/are
(a) D1 only
(b) D2 only
(c) both D1 and D2
(d) none of these
›Reveal solutionSolution
An LED's emission colour (wavelength) is set by the semiconductor's band gap, while its brightness (intensity) is controlled by the forward-bias current.

An LED is a forward-biased p-n junction made of a direct band-gap semiconductor. When forward biased, electrons and holes are injected across the junction and recombine, releasing energy as photons.

Wavelength: the photon energy released on recombination $\approx$ the band gap energy $E_g$ , so $\lambda = hc/E_g$ — set by the material's energy gap. …
Start your 14-day free trial to see the full solution →
CBSE 2020Set ANNUAL1 markMCQ
$Q. Type of material which emits white light in LED :$
(a) GaInN
(b) SiC
(c) AlGaP
(d) GaAsP
›Reveal solutionSolution
Among the given semiconductor compounds, GaInN (Indium Gallium Nitride) is the material used in white-light-emitting LEDs.

Working

Different LED materials emit different colours depending on their band gap:

GaInN (Gallium Indium Nitride): emits blue/UV light efficiently and, combined with a yellow phosphor coating (or by combining red/green/blue chips), is the standard material used to produce white-light LEDs. …
Start your 14-day free trial to see the full solution →

←Previous questionQ22 — What do you mean by current amplification factor β for a transistor? D…→Next questionQ24 — Draw the circuit diagram, how you can form an AND and an OR gate using…

Q.Draw the I-V characteristic curves of a light emitting diode (LED) for yellow and green light. On what factors do the wavelength and intensity of the light emitted by an LED depend?

Concept understanding — Light Emitting Diode (LED)

Q.Draw the I-V characteristic curves of a light emitting diode (LED) for yellow and green light. On what factors do the wavelength and intensity of the light emitted by an LED depend?

🎓Unlock everything free for 14 days

Unlock everything free for 14 days