NatSci2 under Mr. Pili: Light

8/7/2019 NatSci2 under Mr. Pili: Light

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- the classification of electromagnetic wavesaccording to frequency.

The Electromagnetic Spectrum

Types of Electromagnetic Waves Frequency Range(Hz)

Radio Wave 1million

Microwave 1 billion

Infrared 1 trillion

Visible Light 100 trillion

Ultraviolet Gamma Rays 1 million trillion


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- allowing light to pass through with littleor no interruption or distortion so that

objects on the other side can be clearlyseen.

Examples:

water and glasses, etc.

Transparent Materials


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-impervious to light, so that imagescannot be seen through it.

- materials which does not allowthe passage of light, thus imagescannot be seen through it.

Exampleswood, steel, paper, etc.

Opaque Materials


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- property causing visual sensation: theproperty of objects that depends on the

light that they reflect and that isperceived as red, blue, green, or othershades.

- the colors we see depends on thefrequency of light we see.

Color


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red (lowest)

orangeyellowgreenblue

indigoviolet (highest)

Colors According to Frequency

(lowest to highest)

The color spectrum


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White (Composite ofColors)


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Perception of the different colors of Opaque

Materials- the colors we see on different objects depends

on the frequency or the color of light that they

reflect. ( Selective Reflection)

Opaque Material


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Example (Selective Reflection)


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- the color of transparent materialsdepends on the color of the light it

transmits. (Selective Transmission)

Perception of Colors of Transparent Materials


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ReflectionofLight

the return of light rays from a surface in

such a way that the angle at which a givenray is returned is equal to the angle at which

it strikes.


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Formation of Image by Reflection


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the angle of incidence is equal to the angleof reflection (law of reflection)

it give color to all sorts of objects

it happens through vibration of the

electrons of the atoms upon getting forcedinto vibration by the incident vibrating

electric fields of the illuminating light. White

objects reflects all frequencies of light.

when the reflecting surface is rough, theresult is diffuse reflection where the law of

reflection no longer hold true.

PropertiesofReflection


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RefractionofLight

the bending of light when it passesthrough one medium to another.


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1. caused by the changing of the speed of light as it

passes through from one transparent medium to

another.

2. Explains the apparent bending of a stick partlyimmersed in water.

3. Explains the occurrence of mirage (ex.wet

appearance of a distant portion of a concrete road in

a hot sunny day)

4. Explains the late disappearance of sunlight even

after sun set .

Properties of Refraction


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Refractionoflight by Water


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Apparent Location (due torefraction)


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FormationofMirage (due to Refraction)


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Dispersion

refers to the separation of light into colors

according to frequency.


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1. caused by double refraction due to

different speeds of the differentfrequencies of white light of which it is a

composite of.

2. explains the phenomenon of rainbowwith water droplets acting as tiny prisms.

Associated facts


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Formationofrainbow by dispersionofLight


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Total Internal Reflection

refers to the all-reflection

phenomenon of light along anoptical medium, thus a complete

absence of transmission out the

medium.


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1. basis of the proper cutting or facets on a diamond

surface so that it glitters when total international

reflection inside.

2. underlies the operation of optical fibers such as the

one used in a Christmas tree as well as for signal

transmission purposes, replacing the bulky and

expensive copper wires.

Practical Applications


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Fiber Optics

(application)


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Emission Spectra

-- visual record of the wavelengths of the radiationvisual record of the wavelengths of the radiationor particles emitted by a substance, used as aor particles emitted by a substance, used as a

means of analyzing its physical properties such asmeans of analyzing its physical properties such as

energy and mass.energy and mass.


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SourcesofEmission Spectra

A continuum spectrum results when the gas

pressures are higher. Generally, solids, liquids, ordense gases emit light at all wavelengths when

heated.


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Emission

Absorption


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- emission spectra are produced by thin gases in whichthe atoms do not experience many collisions (because of

the low density). The emission lines correspond to photons

of discrete energies that are emitted when excited atomic

states in the gas make transitions back to lower-lyinglevels.

Emission Absorption


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- anabsorption spectrum occurswhenlight passesthrough a cold, dilute gas and atoms in the gas absorbat characteristic frequencies;since the re-emitted lightis unlikely to be emitted in the same direction as the

absorbed photon, this givesrise to dark lines (absenceoflight) in the spectrum.


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Explain the following

1. Explain how papers, garments, wood,etc.obtained their different colors.

2.Explain how the emissionspectrum isused to identify elementswithincompounds.

3. Explain how different glassesobtainedtheir different colors.


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LASER

Light Amplification by Stimulated Emission of Radiation

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NatSci2 under Mr. Pili: Light