elec opt arts

8/11/2019 Elec Opt Arts

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Electric Bulb

1. Outline of Glass bulb

2. Low pressure inert gas (argon, nitrogen, krypton, xenon)

3. Tungsten filament

4. Contact wire (goes out of stem)

5. Contact wire (goes into stem)

6. Support wires (one end embedded in stem; conduct no current)

7. Stem (glass mount)

8. Contact wire (goes out of stem)

9. Cap (sleeve)

10. Insulation (vitrite)

11. Electrical contact


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Filled with inert gasses like argon

Filament made of tungsten

Conversion electric energy to light by collision andtransition.

High heating (2,200 C) allow filament to emit photons

in visible range Length of filament ~ 2 meters

Properties


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Tube light

Consists of a long glass gas discharge tube. Its inner surface is coatedwith phosphorous and is filled with an inert gas, generally argon, with atrace of mercury.

Mercury vapour gets exited by bombardment of electrons emitted by

filament. The excited mercury atoms produce short-wave ultravioletlight that then causes a phosphor to fluoresce, producing visible light.

Once the conduction of electrons between the electrodes is complete, nomore heating of the filaments is required and whole system works at amuch lower current.


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Most of the electronics depends on

semiconductors


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Categorization on the basis of

conductivity1. Conductors

2. Semiconductors

3. Insulators


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Conductors

Most of the conductors used in electronics are metals

like copper, aluminium and steel. Conductors obeyOhm's law and they have very low resistance.

Therefore they can carry electric currents from place toplace without dissipating lot of power.


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Insulators

Glass, most polymers (plastics), rubber and wood areall examples of insulators. These are materials which

will refuse to carry an electric current. Just as there isno perfect conductor, neither is there a perfect

insulator.


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Semiconductors

Some materials are neither good conductors nor good

insulators, since their electrical characteristics fallbetween those of conductors and insulators. These in-

between materials are classified asSEMICONDUCTORS. Germanium and silicon are two

common semiconductors used in solid-state devices.


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p-type semiconductor


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n-type semiconductor


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Working Principle of LED's


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LED

LED are semiconductor p-n junctions that under forward bias conditions can emitradiation by electroluminescence in the UV, visible or infrared regions of theelectromagnetic spectrum. The qaunta of light energy released is approximatelyproportional to the band gap of the semiconductor.


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Excitation

Electron (excited by the biasedforward voltage) is in the conduction

band

Hole is in valance band

Normally the recombination takes place between

transition of electrons between the bottom of theconduction band and the top of the valance band(band exterma).The emission of light is therefore;hc/= Ec-Ev= Eg(only direct band gap allowsradiative transition)

E

k


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How does it work?

P-n junction ElectricalContacts

A typical LED needs a p-n junction

Junction is biased to produce even moree-h and to inject electrons from n to p forrecombination to happen

There are a lot of electrons and holes atthe junction due to excitations

Electrons from n need to be injected to pto promote recombination

Recombinationproduces light!!


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When a light-emitting diode is forward biased (switched on),electrons are able to recombine with holes within the device,releasing energy in the form of photons.


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Electric Heater (electrical energyHeat)

Joules Law:

Electric heating is any process in whichelectrical energy is converted to heat.Common applications include heating ofbuildings, cooking, and industrialprocesses.

An electric heater is an electricalappliance that converts electrical energyinto heat. The heating element insideevery electric heater is simply anelectrical resistor, and works on the

principle of Joule heating:an electriccurrent flowing through a resistorconverts electrical energy into heatenergy.


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Optics


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Reflection


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Refraction


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Total Internal Reflection


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Differaction from a Prism


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Rainbow formation


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Total internal reflection


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contd...

The critical angle for this water-air interface is 48.75 degrees.When the angle of incidence is greater than the critical angle,

no refraction occurs. Instead, the incident beam is reflected,

obeying the Law of Reflection. This is called Total internalreflection.In the formation of a rainbow, Total Internal Reflection occursat the rear of the raindrop - the water-to-air interface.

Therefore, in order for a rainbow to be visible, the angle ofincidence at that interface must be greater than the critical

angle.


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(L)ight (A)mplification by(S)timulated (E)mission of (R)adiation


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Properties of Laser Light

Laser light is:

Approximately monochromatic(single color wavelength)

Coherent(wavelengths in phase)

Collimated(non-divergent)


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Coherence


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Collimated Light

Non-collimated Light Collimated Light


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The Bohr atom and a simple energy-level diagram


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Color of Laser

C d


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Contd


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A four-level laser pumping system


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Schematic diagram of a basic laser


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Telescope


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Contd

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