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If the diode is reverse-biased, the + terminal of the battery is connected to the n-type semiconductor. This makes it even more negatively charged. It also removes even more of the free electrons near the depletion band. At the same time, the - terminal of the battery is connected to the p-type silicon. This will supply free electrons and fill in more of the holes next to the depletion band. Both processes cause the depletion band to get wider. The resistance of the diode (which was already high) increases. This is why a reverse-biased diode does not conduct.

Another explanation for the increased resistance is that the battery has made the p-type semiconductor m ore negative than it used to be, making it repel any electrons from the n-type semiconductor which attempt to cross the depletion band.

On the other hand, if the diode is forward biased, the depletion band is made narrower. The negative charge on the p-type silicon is cancelled out by the battery. The greater the voltage used, the narrower the depletion band becomes. Eventually, when the voltage is about 0,6 V (for silicon) the depletion band disappears. Once this has occurred, the diode conducts very well.

The diode

  1. What is a diode?
  2. What is a diode made of?
  3. What is the term which means that a diode is connected the `wrong way' and little current is flowing?
  4. Why is a diode able to conduct electricity in one direction much more easily than the other?

The light-emitting diode (led)

A light-emitting diode (LED) is a diode device that emits light when charge flows in the correct direction through it. If you apply a voltage to force current to flow in the direction the LED allows, it will light up.

Symbol for a light-emitting diode with anode and cathode labeled.

Circuit symbols

This notation of having two small arrows pointing away from the device is common to the schematic symbols of all light-emitting semiconductor devices. Conversely, if a device is light-activated (meaning that incoming light stimulates it), then the symbol will have two small arrows pointing toward it. It is interesting to note, though, that LEDs are capable of acting as light-sensing devices: they will generate a small voltage when exposed to light, much like a solar cell on a small scale. This property can be gainfully applied in a variety of light-sensing circuits.

The colour depends on the semiconducting material used to construct the LED, and can be in the near-ultraviolet, visible or infrared part of the electromagnetic spectrum.

Interesting fact

Nick Holonyak Jr. (1928) of the University of Illinois at Urbana-Champaign developed the first practical visible-spectrum LED in 1962.

Light emission

The wavelength of the light emitted, and therefore its colour, depends on the materials forming the p-n junction. A normal diode, typically made of silicon or germanium, emits invisible far-infrared light (so it can't be seen), but the materials used for an LED can emit light corresponding to near-infrared, visible or near-ultraviolet frequencies.

Questions & Answers

what is an isomer?
Kiba Reply
organic compounds with the same molecular formula but different structural formula
liphelo
how is frequency directly proportional to kinetic energy max. and what is the relationship between the wavelength and the energy of a photon. eg if a photon with a greater wavelength and a photon with less frequency. what would be the energies. as in which one would be greater and why
Pearl Reply
relationship wave depend n enrgy greadt reflect of energy n the form of tex shape
thulare
what is Cell capacity?
liphelo Reply
what are hydrocarbons
Nyiko Reply
compounds that are made up of hydrogen and carbon only
Patience
They are compounds that consist only with hydrogen &carbon elements.
Duncan
how do i calculate the work done on an object by a frictional force
Emmelda Reply
@ Emmelda it's W = FxCos180 Where 180° is the angle between Frictional force and where the object is going, it's always 180° because it opposes the motion. Then F is the magnitude of the force and x is the displacement
Vukona
Ohm's law state that provide the temperature remains constant, that potential difference is directly proportional to the current flowing in the circuit
Ezile Reply
state ohms law
Booi
what does ohm's law state ?
Gugu Reply
ohm's law state that the potential difference across a conductor is directly proportional to the current in the conductor at constant temperature
Nqobile
ohm'law in metalic conductor is directly proportional to the potential difference provided the temparature
Nandise
what is the principle on which generator is based
Nqobile Reply
electromagnetic induction
Sethu
Explain it😌
Nelisa
mechanical​ energy is used to rotate turbines inside the generator where a coil placed between two fixed magnets.as the coil rotates it cuts the magnetic flux due to the magnets. the magnetic flux will then induce an electric current into the coil which will be transmitted to the brushes
Ruva
may you Please instruct me on how to do Flemmings Right hand dynamo Rule
Siphe
Fleming's right-hand rule shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field. It can be used to determine the direction of current in a generator's windings
Ruva
 hold out the right hand with the first finger, second finger and thumb at the right angle to each other.forefinger represents the direction of the line of Force, the thuMb points in the direction of Motion or applied force, then seCond finger points in the direction of the induced Current
Ruva
what is spectrum
Mpeh Reply
It is a different combinations of frequency of light or any types of waves.
Duncan
Heii guys what's the topic? Am neww
Vannessa Reply
In nuclear reactions, is it necessary that there must only be one element on the product side and a radioactive particle or you can have a product that are both radioactive particles?
Jobena Reply
conservative force is a force when the work done in moving the object between the two points that does not depend on the path way
Bongiwe Reply
what is conservative force?
Mh Reply
It is a force , that does not have any external features affecting it
Duncan
what does the alternating current do
Kwanga Reply
what is definition of hydrocarbon
jessha Reply
it is the atoms that Contain of C atoms and H atoms only
Xolani
You mean molecules
Jc
yea 💯
Xolani
what's the definition of le chatelier?
Karabo
what is electromagnetic
Daniel
differentiate between DC motor and Ac generator
Kwanga
dc motor converts electrical energy into mechanical energy while ac generator converts mechanical into electical
Ophola
DC has a Split-ring but then Ac has a slip-rings.
Joyous
what's the other name of galvanic cell?
Cwenga
galvanic cell is also called Voltanic cell
Bongiwe
is the chain whereby there is only Hydrogen and Carbon atoms only.
Hlonny
what is the difference between AC and DC moto
Mihle
please check the answer from Ophola and Joyous
Nomsa
AC motor consists of 2 slip rings and a DC motor has a single split ring commutator
Vukona
ac have slip rings n DC has split rings
mudodzwa

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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