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महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर

महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर में इको ट्रेल 30 नवम्बर को राजस्थान वन विभाग उदयपुर डिविजन तथा WWF-India उदयपुर डिविजन के सानिध्य में महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर में इको ट्रेल की गई, जिसमें WWF-India के स्टेट काॅर्डिनेटर श्रीमान अरूण सोनी तथा वन विभाग कीे ओर से डाॅ. सतीश कुमार शर्मा, सेवानिवृत्त अधिकारी मौजूद थे। मुझे भी इस इको ट्रेल में जाने का सुअवसर प्राप्त हुआ, जो गोरीला व्यू पाॅइंट से बड़ी-लेक व्यू पाॅइंट तक की गई इसमें मुझे विज्ञान की एक नई शाखा के बारे में पता चला, जिसे टट्टी विज्ञान कहा जाता है। सुनने में आपको थोड़ा अजीब लगेगा, मुझे भी सुनकर हैरानी हुई, परन्तु वास्तव में एक ऐसा भी विज्ञान है, जिसके बारे में डाॅ. सतीश शर्मा ने बड़े ही विस्तार पूर्वक बताया कि किस प्रकार वनों में जानवरों की टट्टी देखकर यह पता लगाया जा सकता है कि यहां कौनसा जानवर आया था। जानवरों की टट्टी कितनी पुरानी है, वह गीली है या सूखी है। इसी के आधार पर उस विशेष जंगल में कौन-कौनसे जानवर विचरण करते हैं, उसके बारे में वन विज्ञान के कर्मचारी पता लगा लेते हैं। जानवरों की टट्टी का विश्लेषण करके यह पता लगा...
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Light emitting diode | Electronics | Semiconductor diode

Optoelectronic diode

  • An optoelectronic diode is a diode which includes optics along with electronics. It means optoelectronic diode either emit light or they work when light falls on them.
  • Here we will discuss about light emitting diode as an optoelectronic diode.

Light emitting diode (LED)

Principle of LED

  • In simple p-n junction diodes (Ge, Si), the energy bands are indirect.
  • When these diodes are forward biased, then the recombination of electron-holes across the junctions starts.
  • When electron jumps from higher energy level to lower energy levels then the energy emitted by electrons in these diode will be in the form of heat and hence we can not see it.
  • In some semiconductor (GaAs), the energy bands are direct.
  • When these semiconductor diodes are forward biased then in the process of recombination of electron-hole pairs, the electron jumps from higher energy level to lower energy levels.
  • The energy emitted during this process lie in the visible region, and it is clearly seen due to transparent material of the crystal.
  • Since these diodes emit light energy on forward biased, hence they are known as light emitting diode.

Construction of LED

Light emitting diode (a) Arrangement and (b), (c) Circuit symbol
  • In LED generally we use GaAs or In-P.
  • In these diodes n-type semiconducting layer grow on a p-type substrate by diffusion.
  • After it a thin layer of p-type material is grow up on n-type layer.
  • At the external sides of these layers a thin metallic contacts are attached, which are connected to cathode (K) and anode (A) respectively.
  • The whole arrangement is placed in a transparent plastic cover or envelope.
  • The colour of plastic cover depends on the light emitted by diode.
  • It is used in low forward bias.
  • The wavelength (colour) emitted by the diode depends on the the % error of As in GaAS-P diode.
  • Common formula for it is GaAs1-x Px.
  • GaAs gives I.R. light and GaP gives light of blue colour.
  • If the energy band of above diode is 1.8 eV, we get light of red colour.
  • If this diode is doped with nitrogen we get light of all the colours ranging from yellow to green in visible region.
  • Wavelength of emitted light
                λ= hc / Eg = (1.26 / Eg) μm
  • Here h = Planck's constant, c = velocity of light and Eg = energy gap between valence band and conduction band.
  • If we join seven segment of LED, then we can get any number from 0 to 9. Here a number 4 and number 8 are shown.
Seven segment LED

Uses of LED

  • LED is used in calculators.
  • It is used in watches.
  • LED is also used in platform signals.
  • Light emitting diode is also used as a pilot lamp in electronic device for showing on-off position.
  • Theses diodes are also used in optical communication systems.
To know more about light emitting diode (LED) please click on the link https://youtu.be/EyTUJV-NXH0  for English and on https://youtu.be/WuOKbuHpq1Q  for bilingual (Hindi/English)
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