LightThe Nature and Colors of Light

The Electromagnetic Spectrum

Light waves are electromagnetic wavesLight waves consist of periodically changing electric

and magnetic fieldsProduced by accelerating charged particles

The Electromagnetic Spectrum

The complete range of frequencies and wavelengths of EM waves

Visible light is only a small portion of the spectrumVarious kinds are classified according to the

methods by which they are generated or received

https://classconnection.s3.amazonaws.com/255/flashcards/4013255/jpg/electromagneticspectrum-141B490BAC872789434.jpg

Speed of Light

c represents the speed of light

c = 3.00x108 m/s

The speed of light in a material is always less than c

v=fλ applies to light waves

Reflection

Wave changes direction upon hitting a

reflecting surface

0ri

R

N

I

R= reflecting rayr= angle of reflectionI= incident rayi= angle of incidenceN= normal

Law of Reflection

θi= θr

States that waves are reflected from the boundary of the medium at the same angle at

which they strike it

Refraction

Wave changes direction upon

entering a medium of different density

Absolute index of Refraction

n is the ratio of the speed of light in a vacuum, c, to the speed of light in a material medium, v

n=c/v

http://sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and-sight/sci-media/images/refraction-of-light-in-water/685295-1-eng-NZ/Refraction-of-light-in-water.jpg

Example

If a ray of light enters the glass-air boundary and if the n for glass is 1.52 and n for air is 1.0003, a) what will be the path of light? Create a diagram and label the media; b) in which medium will the light ray travel faster?

https://upload.wikimedia.org/wikipedia/commons/8/85/Refraction_photo.png

http://sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and-sight/sci-media/video/refraction/668954-1-eng-NZ/Refraction.jpg

Dispersion

Speed of light in a material in different substances is

different for different wavelengths

The index of refraction of a

material depends on wavelength

The dependence of wave speed and index of refraction

on wavelength is called dispersion

In most material, n inc with decreasing wavelength and inc f

Light of longer wavelength has greater v than light of shorter wavelength

In the visible light in a prism, violet light is deviated most and red light is deviated least

Light spreads out and it is said to be dispersed into a spectrum

Dispersion

DispersionThe amount of

dispersion depends on the difference between the

refractive indexes for violet light and for red

lighthttp://bolvan.ph.utexas.edu/~vadim/Classes/2014f/Prism1.jpg

the science of color

ROYGBIV

Basic Color Principles

Color dimensions

vary

Color dimensions

vary

Additive Primary Colors

These three colors can approximate, through

selective mixture, all of the other colors.

BLUE

RED GREENW

Secondary Colors

Each is placed between the two primaries that are mixed to produce itM C

Y

Primary & Secondary Colors

Red Blue Magenta

Primary & Secondary Colors

Red Green Yellow

Primary & Secondary Colors

Green Blue Cyan

SCATTERING OF LIGHTColors and the colors of the atmosphere

Scattering of Light• The absorption and re-

radiation of light in a variety of directions is called scattering

• Scattering of light depends on λ

Scattering of Light: Why the sky is blueThe intensity of light scattered from air molecules is inversely proportional to the fourth power of the λ

Intensity ratio for the 2 ends of the spectrum: (700nm/400nm)4= 9.4

Scattering of Light: Why the sky is white

Clouds contain high concentration of water droplets

Light of all wavelengths are scattered out of the cloud, so the cloud looks white

Scattering of Light: Why sunsets are red?

Light has to travel longer distance

A substantial fraction of the blue light is removed by scattering: W-B= Y or R