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What is Light?

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Properties of Waves

All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s

trough

crest

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Wavelength

(length/cycle)

Wavelength (l): the length of one complete cycle

trough

crest

Properties of Waves


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Wavelength

(length/cycle)

Amplitude: 1/2 height between trough and crest

Amplitude

trough

crest

Properties of Waves


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Wave Speed = wavelength x frequency

Wave Speed= f

(length/second) = (length/cycle) x (cycle/second)

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Light as a Wave

Light waves are characterized by awavelength l

and afrequency f

c = 300,000 km/s = 3108m/s

l

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Electromagnetic Waves

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Light as a Wave

Wavelengths of light are measured in units ofnanometers (nm) or ngstrm ():1 nm = 10-9m

1 = 10-10m = 0.1 nm

Visible lighthas wavelengths between4000 and 7000

(400 nm700 nm).

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The Electromagnetic Spectrum

Need satellites toobserve

Wavelength

Frequency

High flyingair planes

orsatellites

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Wavelengths and Colors

Differentcolors of visible light correspond

to different wavelengths.

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Visible Light (VIS)

700 to 400 nm

Our eyes are sensitive to this region of thespectrum

Red-Orange-Yellow-Green-Blue-Indigo-Violet

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In other words,

waves withshorter

wavelengths(or higher

frequency) have

higher energy

Light as Particles

Light can also behave like a stream of particles, calledphotons

A photon has a specific energy E,

Energyis proportional to frequency and inversely

proportional to wavelengthE = hf

h = 6.626x10-34J*s is the Planck constant.

The energy of a photon does notdepend on the intensityof the

light!!!

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Solar

Radiation

The Source for

99.9% of Earths

Energy

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Solar Spectrum

The sun emits radiation at allwavelengths

Most of its energy is in theIR-VIS-UV

portions of the spectrum

~50% of the energy is in thevisibleregion

~40% in the near-IR~10% in the UV

Wavelength (m)

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RADIO WAVES

Have the longestwavelengths andlowest frequencies of all the electromagneticwaves.

A radio picks up radio waves through

an antenna and converts it tosound waves. Each radio station in an area broadcasts

at a different frequency. # on radiodial tells frequency.

MRI(MAGNETIC RESONACE IMAGING) Uses radio waves with a

magnet to create an image

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MICROWAVES

Microwaveshave the shortest wavelengthsand the highest frequency of the radio waves. Used in microwave ovens.

Waves transfer energy to the water in the food causingthem to vibrate which in turn transfers energy in theform of heat to the food.

Used by cell phones and pagers.

RADAR(Radio Detection and Ranging) Used to find the speed of an object by sending out radio

waves and measuring the time it takes them to return.

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INFRARED RAYS

Infrared= below red Shorter wavelength and higher

frequency than microwaves. You can feel the longest ones

as warmth on your skin Heat lamps give off infrared

waves. Warm objects give off more

heat energy than cool objects. Thermograma picture that

shows regions of differenttemperatures in the body.Temperatures are calculatedby the amount of infraredradiation given off. Thereforepeople give off infrared rays.

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VISIBLE LIGHT Shorter wavelength and higher frequency than infrared rays. Electromagnetic waves we can see. Longest wavelength= red light

Shortest wavelength= violet (purple) light

When light enters a new medium it bends (refracts). Each

wavelength bends a different amount allowing white light toseparate into its various colors ROYGBIV.

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ULTRAVIOLET RAYS

Shorter wavelength and higher frequency thanvisible light

Carry more energythan visible light Used to kill bacteria.(Sterilization of equipment)

Causes your skin to produce vitamin D(good forteeth and bones)

Too much can cause skin cancer. Use sun block to protect against (UV rays)

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X- RAYS Shorter wavelength and higher frequency

than UV-rays Carry a great amount of energy Can penetrate most matter. Bones and teethabsorbx-rays. (The light

part of an x-ray image indicates a place

where the x-ray was absorbed)

Too much exposure can cause cancer (lead vest at dentist protects organs

from unnecessary exposure)

Used by engineersto check fortiny cracks in structures. The rays pass through the cracks

and the cracks appear dark on film.

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GAMMA RAYS

Shorter wavelength and higherfrequency than X-rays

Carry the greatest amount of energyand penetrate the most.

Used in radiation treatmentto killcancer cells.

Can be very harmful if not used

correctly.

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SUMMARYAll electromagnetic wavestravel at the

same speed. (300,000,000 meters/secondin a vacuum.

They all have different wavelengthanddifferent frequencies. Long wavelength-lowest frequency

Short wavelength

highest frequency The higher the frequency the higher the

energy.

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