Light & EM Spectrum

Properties of Light

Light travels at high speeds

3 x 108 m/s300,000 km/s

1.08 x 1011 km/h108 billion km/h

Properties of LightLight travels in straight lines

Properties of Light

Heat and electricity require a medium for transmission.

Particles in a physical substance carry the energy being transmitted.

Transfer of Heat of Energy

http://cookwilkie11.wikis.birmingham.k12.mi.us/file/view/Convection-Conduction.jpg/275567456/Convection-Conduction.jpg

Conduction

• The process by which heat or electricity is directly transmitted through a substance

• Conditions:– a difference of temperature or electrical

potential between adjoining regions– without movement of the material

• Some examples of conduction:– sound waves– transmission of impulses along nerves

Convection

• Movement of molecules within fluids– Transmission of heat in a fluid or gas by the

circulation of currents• Fluids:

– liquids, gases– Can not be solids

• Vertical movement of heat and moisture– Hotter, less dense materials rise– colder, denser material to sink under the influence of

gravity• Example: Weather patterns due to updrafts and

downdrafts in an unstable air mass

http://globalmicrowave.org/content/atmosphericl_convection.jpg

http://www.ux1.eiu.edu/~cfjps/1400/FIG07_006.jpg

http://3.bp.blogspot.com/-ZSVl3YFwDDo/Tycy3SXjXkI/AAAAAAAAAD4/t1XEXbaznOw/s1600/cond_conv_rad_small.jpg

Properties of Light

Unlike heat or electricity, light can travel through space

without any medium.

Light Waves

Light energy travels in waves.

Waves are vibrations that transfer energy from place to place without matter being transferred.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/radiation/anintroductiontowavesrev1.shtml

Light Waves

Light has an electric and magnetic fieldLight is an electromagnetic waveLight transfers energy through electromagnetic

radiationElectromagnetic radiation is a method of

transferring energy by vibrating electric and magnetic fields

Properties of Waves

In our discussion of the changes in wavelength of light waves, we will assume a constant amplitude.

Wavelength

Wavelength

Amplitude

Amplitude

http://www.kollewin.com/blog/electromagnetic-spectrum/

Electromagnetic Spectrum

http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg


The shorter the wavelength…

• Higher frequency

• Higher energy

Animation of wavelength and frequency relationship

•http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/radiation/anintroductiontowavesrev2.shtml

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/radiation/anintroductiontowavesrev2.shtml

http://ebookbrowse.com/sura-electromagnetic-spectrum-full-chart-pdf-d14713735

Electromagnetic Spectrum Application

Radio Spectrum (9 Hz – 275 GHz) Frequency Allocations in Canada (2007)

Divided into frequency bands, each with characteristics peculiar to it which determine the appropriate usage. Each band has been allocated by international agreement at a World Radiocommunication Conference (WRC) to one or more service or usage. After WRC, Industry Canada allocates specific frequency bands to satisfy domestic communications requirements.

For better details see original Government of Canada document: http://www.ic.gc.ca/eic/site/smt-gst.nsf/vwapj/spectallocation-08.pdf/$FILE/spectallocation-08.pdf

Visible Spectrum

• Although light is a visible form of energy, most of the light energy that surrounds us is invisible

• Humans can only detect light within a very narrow range of wavelengths (~400-700 nm)

• The range of light waves that we can see is known as the visible spectrum

Visible Spectrum

http://www.astro.virginia.edu/~rsl4v/PSC/Images/em.jpg

Visible Spectrum• Colours we see correspond to a specific

wavelength on the electromagnetic spectrum• Colours are what makes up the visible spectrum

ROY G BIV

Additive Colour Theory

(for LIGHT)

Subtractive Colour Theory

(for PIGMENT)

ColourColour

White light is composed of different colours (wavelengths) of light


Prism• In a vacuum, each wavelength of

light travels at the same speed• A prism will slow down each

wavelength of light at different rates– Red light (longest wavelength,

least energetic) is slowed the least

– Violet light (shortest wavelength, most energetic) is slowed the most

• When wavelengths of light travel at different speeds, they will be visible separately into their individual colours


It is possible to produce white light by combining the three primary colours of light:

• Red• Green• Blue


If you mix two primary colours together, you will make a secondary colour

Secondary Colours of light:• Magenta• Yellow• Cyan

Primary Colours of Light make up a computer monitor

Primary & Secondary Colours

Additive(all light sources)

Subtractive(all pigments)


Primary Colours:• Cyan• Magenta• Yellow

Secondary Colours:• Red• Green• Blue

Primary Colours:• Cyan• Magenta• Yellow

Secondary Colours:• Red• Green• Blue

Printer Ink


Coloured objects absorb some wavelengths (colours) of light and reflect the rest which is what we see.

Colour Theory

• White light is the combination of all the colours reflected into our eyes

• Colours detected by the eye are due to wavelengths being reflected off the object

• Colours undetected by the eye are due to wavelengths being absorbed by the object

• White objects reflect all colours

• Black objects absorb all colours

Bill Nye Video Light & Colour Questions for part 1 (0:50-2:45, 3:45-4:12, 5:15-end)http://www.youtube.com/watch?v=gtgBHsSzCPE&feature=related

1. What is white light?2. What does a prism do to white light?3. Why can’t a prism break up red light into other colours like it can do

to white light?4. What gives fruits and vegetables all their different colours?5. What colour(s) is the skin of a red apple absorbing?6. What colour is the skin of a red apple reflecting?7. What happens to all the colours of white light when it hits a black

object ?8. What is the function of pigments in paints?9. How do you get black paint?10. Why does mixing all the colours of paint give you black instead of

white when white light is a mixture of all colours?See next slide for 2 more questions from part 3 of video

Bill Nye Video Light & ColourQuestions for part 3 (0-1:45)

http://www.youtube.com/watch?v=bPyWooEpwXw&feature=PlayList&p=34CAF189A5C0F7B9&playnext_from=PL&playnext=1&index=1

1. Why is the sky blue?

2. Why does water look blue?

Optional for part 3: clip on Crayola follows 1:45

Optional for your viewing interest: part 2 http://www.youtube.com/watch?v=bPyWooEpwXw&feature=PlayList&p=34CAF189A5C0F7B9&playnext_from=PL&playnext=1&index=1

• information on neon lights and lasers

Multiwavelength

Multiwavelength• Visible light provides only limited information about our universe. • Information from the ‘invisible’ parts of the electromagnetic

spectrum has provided a lot of exciting and surprising discoveries.

• Gallery of astronomical images of objects in multiple wavelengths of the EM spectrum

• http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/

• Slideshow of the sun in different wavelengths compared to hearing Beethoven’s 9th in different frequencies

• http://ccnmtl.columbia.edu/projects/helfand/

• Multiwavelength Universe Poster• http://teachspacescience.org/graphics/pdf/10000729.pdf

Light & EM Spectrum

Education

Transcript of Light & EM Spectrum