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Objectives
What is a wave?
Define, write the symbol for, and write the units for each of the following: wavelength,
frequency, and speed (velocity). Define and give the abbreviation of an Ångstrom. Review the
definitions and abbreviations of the metric prefixes giga, mega, kilo, centi, milli, micro, and nano
so that you can define, know the meaning of and give the symbol for each.
For a sound wave, which wave property corresponds to pitch?
Use the terms longer, shorter, higher, and lower to compare a high pitch sound to a low pitch
sound in terms of their frequency and wavelength.
Is a blue flame hotter or cooler than the red rod it is heating?
Use the terms higher, lower, greater, lesser, longer and shorter to compare the light from the
red rod to the light from the blue flame in terms of their energy, frequency, wavelength, and
temperature.
State the colors of the visible spectrum in order from coolest to hottest.
If you see a red star and a blue star, what can you conclude?
What color do astronomers and others use to portray high intensity? Low intensity?
State the approximate wavelengths of red and violet (blue) light in both Ångstroms and nm.
If you detect an astronomical object emitting short wavelengths, what can you conclude?
What does the color of a star or hot dense object tell you?
Name the seven types of EM radiation in order from lowest to highest f, from longest to shortest
wavelength, from lowest to highest energy.
Watch the video “Infrared: More than Your Eyes Can See” (link on last slide). State one
advantage that IR astronomers have. State one disadvantage.
Waves
Wave Properties
Electromagnetic (EM) spectrum
Wave = Periodically repeating disturbance
Examples
Waves
Periodically repeating disturbance
Example – siblings!!!
Photo from www.3genfamily.com
Wave Properties (How to describe waves)
Show traveling wave
http://www.animations.physics.unsw.edu.au/jw/travelling_sine_wave.htm
Jump rope demo
Some general wave properties
1. Velocity (speed)
 Define:
How fast the wave moves,
or Distance/time
Some general wave properties
1. Velocity (speed)
 Definition: How fast…
 Symbol: v
 Units:
m/s, mi/h (MPH) , ft/s, …
Note: m vs mi
Some general wave properties
1. Velocity (speed)
 Symbol: v
 Units:
m/s, mi/h, ft/s, ...
 Examples:
Light waves in space (speed of light)
= 186 000 mi/s = 3.0 x 108 m/s
Speed of sound in air (at sea level)
= 1100 ft/s = 770 mi/h = 340 m/s
Some general wave properties
2. Wavelength
 Define: Distance between similar points
on a wave in the direction of wave travel
Wave
Moves
→
Waves
2.
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Some general wave properties
Wavelength
Definition: Distance between
peaks or troughs of a wave
Symbol:  (lambda)
Units: m, mi, ft..., nm, m,
Ångstrom (1 Å = 10-10 m)
Examples: Red light
 = 700 nm = 7000 Å
Blue (violet)  = 400 nm = 4000 Å
Middle C
 = ~1 m
Use “longer” and “shorter” to describe .
Example-Red light has a longer  than blue.
Waves
Some general wave properties
3. Frequency
 Define: Number of oscillations (cycles) per
second
 Example: swinging
Waves
Some general wave properties
3. Frequency
 Symbol: f
 Units:
cycles per second (cps),

Hertz (Hz) = 1 cps
 Example: 88.5 MHz (car radio)
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Middle C f ~ 260 Hz
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For sound, frequency corresponds to pitch.
 Use “high” and “low” to describe frequency and
pitch. Example-Sopranos sing at high
frequencies but basses sing at low frequencies.
Waves
Some general wave properties
4. Energy
Define: Ability to make something happen
(ability to do work)
http://www.flyingturtle.org/energy/definition.html
Waves
Describing waves
How are f and pitch related?
Frequency varies with Pitch
f = pitch
high f = high pitch
low f = low pitch
Waves
Describing waves – Video
https://www.youtube.com/watch?v=24BVa2Hj_e4
How are f and λ related?
Frequency varies with 1/wavelength
(inverse relationship)
f varies with 1 / λ
high f = short λ
low f = long λ
Waves
Describing waves –
Write a sentence or two comparing the
wavelength and frequency of a higher
pitch sound to a lower pitch sound. Use
the words higher, lower, longer, shorter,
frequency, wavelength.
Waves
Describing waves –
Write a sentence or two comparing the
wavelength and frequency of a higher
pitch sound to a lower pitch sound. Use
the words higher, lower, longer, shorter,
frequency, wavelength.
Example: The higher pitch has a higher
frequency and shorter wavelength.
Waves
Describing waves –
 Hearing check
https://www.youtube.com/watch?v=H-iCZElJ8m0
 Humans



can hear from 20 Hz to 20 000 Hz
After 30: about 15 000 Hz
After 70: about 6 000 Hz
Human speech up to 8 000 Hz
Waves
Which is hotter?
A reddish star or a blue-ish star?
BLUE STAR
IS HOTTER!
Waves
Observe: Flame color differences
Which part of the flame
is hotter?
BLUE
IS HOTTER!
Wikipedia.com
Waves
Observe: Metal glow color differences
Which color of the heated
metal is hotter?
http://upload.wikimedia.org/wikipedia/commons/a/a9/Hot_metalwork.jpg
Waves
HEAT COLORS
MILD STEEL
2500 F
1371 C
MAXIMUM HEAT FOR WROUGHT IRON FORGING,
STAINLESS STEEL MELTS (2400 to 2700 F)
2400 F
1316 C
MILD STEEL BURNS, CARBON STEEL MELTS 2400 (HIGH)
TO 2750 (LOW CARBON) F, GLASS MELTS 2377 F
2300 F
1260 C
MILD STEEL MAXIMUM FORGING TEMPERATURE & FORGE
WELDING HEATS
2200 F
1204 C
2100 F
1149 C
GREY CAST IRON MELTS FROM 2100 TO 2350 DEGREES F
2000 F
1093 C
GOLD MELTS @ 1945 DEGREES F
1900 F
1038 C
COPPER, BRASS, BRONZE MELT 1652 TO 1981 DEGREES F
1800 F
982 C
SCALE FALLS OFF IRON FREELY @ 1750 DEGREES F,
GLASS MELTS 1800 TO 2200 DEGREES F
1700 F
927 C
SILVER MELTS @ 1761 DEGREES F
1600 F
871 C
1500 F
816 C
1400 F
760 C
1300 F
704 C
1200 F
649 C
1100 F
693 C
1000 F
538 C
UNFANNED COALS OF A WOOD FIRE APPROX.
SCALE FORMS AND ADHERES TO IRON, MILD
STEEL MAGNETIC POINT (1420 F)
BORAX MELTS @ 1365 DEGREES F, ENAMELS FIRED AT
1350 TO 1500 DEGREES F
IRON FINISHING HEAT & STRESS RELIEVING, ALUMINUM
MELTS @ 1220 DEGREES F
RED IRON, VISIBLE IN SUNLIGHT, STRESS RELIEVING OF
IRON
RED IRON, VISIBLE IN DAYLIGHT
Waves
http://www.blksmth.com/heat_colors.htm
Video – Heat ice cube with induction heating
https://www.youtube.com/watch?v=aLwaPP9cxT4
Observations:
•Before heating: no color
•While heating: Red to Orange to Yellow
•While cooling: Yellow to Orange to Red to no color
Conclusions: Red is cooler than Orange and Yellow
Waves
Video – Heat temperature rod over gas stove
https://www.youtube.com/watch?v=dZ2Wg7gJ1CA
Observations:
•Before heating: blackish
•While heating: Dark Red to Red to Orange to Yellow
•While cooling: Yellow to Orange to Red to Dark
Red to original color (black)
Conclusions: Red (cooler) to Orange to Yellow
(hottest)
Waves
Conclusions:
•Blue is hot, Red is cooler
•Order of colors from cooler to hotter is:
Red Orange Yellow Green Blue Violet
ROY G. BIV
Waves
Apply conclusions to stars…which is hotter?
A reddish star or a blueish star?
BLUE STAR
IS HOTTER!
Waves
High temperature means fast vibrations of atoms
means high f
means short λ
Red Orange Yellow Green Blue Violet
ROY G. BIV
Longer λ (700 nm)
Shorter λ (400 nm)
Lower f
Higher f
Lower energy
Lower temperature
Higher energy
Higher temperature
Waves
Describing waves –
Write a sentence or two comparing the
energy, temperature, frequency and
wavelength of a reddish star to a bluish
star. Use the words higher, lower, longer,
shorter, frequency, wavelength, energy,
temperature.
Waves
Describing waves –
Write a sentence or two comparing the
energy, temperature, frequency and
wavelength of a reddish star to a bluish
star. Use the words higher, lower, longer,
shorter, frequency, wavelength, energy,
temperature.
Example: The reddish star has a longer
wavelength, lower frequency, lower energy
and lower temperature compared to the
bluish star.
Waves
How color is used
In some visual portrayals, (art or
representations of intensity), red is intense
and blue is less so.
Van Gogh
Waves
How color is used - Centaurus A
Visible
Radio
Red is intense and blue is less so.
Waves
How color is used
Mars -Red is high
and blue is low.
Waves
How is color used here?
NGC 6823 -Read the
caption
Waves
Spectra
Radiation and
Spectra
Spectra
Spectrum – display of color or wavelengths
Spectra - plural
Electromagnetic (EM) Spectrum
 Long λ
Low f
Low energy
Visible
Spectra
ROY
G. BIV
(700 nm) (400 nm)
Short λ 
High f
High energy
Electromagnetic (EM) Spectrum
 Long λ
Low f
Low energy
Sub red
“Feel” not see
Visible
Spectra
ROY
G. BIV
(700 nm) (400 nm)
Short λ 
High f
High energy
Beyond violet
Infrared (IR)
Ultraviolet (UV)
Electromagnetic (EM) Spectrum
 Long λ
Low f
Low energy
Visible
ROY G. BIV
(700 nm) (400 nm)
Short λ 
High f
High energy
<5% of universe
Ralph's Mother Is Visiting Uncle Xavier's Garden
Radio Microwave Infrared Visible Ultraviolet X-ray Gamma
Part of the above from http://library.thinkquest.org/10380/advanced.shtml
Electromagnetic (EM) Waves
Radar TV
FM
AM
Gamma X-ray Ultraviolet Visible Infrared Microwave Radio
Hotter source
Higher energy
Shorter 
V
Higher f
EM spectrum
I B G. Y O R
Cooler source
Lower energy
Longer 
Lower f
Radar TV
Hot source?, E?, ?, f?
FM
AM
Electromagnetic (EM) Spectrum
Light, Radio……… Others????
Radar TV
Shortest Wavelength
1x10-20 m
Ultra High Energy Gamma Rays
FM
AM
Longest Wavelength
possibly up to 1011 m
Ultra Low Frequency Radio
Homework & Observation Update
•
•
•
View the infrared link on YouTube to understand infrared
radiation better: http://www.youtube.com/watch?v=2--0q0XlQJ0
Observations
•
Sunset Part 1 – Due Tuesday, Feb. 14; email by midnight.
•
Moon Phases - Due Thursday, Mar. 2; hand-in or email
picture by midnight
Test 1
•
Grades posted on website
•
Tests will be handed back on Tuesday, Feb. 14