1. Electromagnetic Radiation Electromagnetic Spectrum
Partnership in Math and Science August 2009

2. Waves Medium vibrates parallel to wave direction Sound waves
Compression Waves
Medium vibrates parallel to wave direction
Sound waves
Transverse Waves
Medium vibrates at right angle to wave direction
Electromagnetic waves
Compression waves
Waves and magnetic field
Comparison of compression and transverse

3. Frequency = # of wave crests per second
Wave Characteristics
Frequency = # of wave crests per second

5. Wavelength and Frequency
                    Short wavelength High frequency High energy
                                                                             
                    Long wavelength Low frequency Low energy

6. Wavelength and frequency
Higher the frequency = Shorter the wavelength
The speed of electromagnetic radiation is equal to the speed of light

7. All objects emit electromagnetic radiation
Temperature of an object = sum of all radiation emitted at each wavelength
Hot objects emit more of their radiation at short wavelengths [short wavelength = higher energy]
Cool objects emit more of their radiation at long wavelengths [long wavelength = lower energy]

8. Black bodies
A black body is an idealized object that absorbs all electromagnetic radiation that falls on it.
No electromagnetic radiation passes through it and none is reflected
If no light (visible electromagnetic radiation) is reflected or transmitted, the object appears black when it is cold.
A black body emits a temperature-dependent spectrum of light -- this thermal radiation from a black body is termed black-body radiation

9. Black body radiation
At room temperature, black bodies emit mostly infrared light, but as the temperature increases past a few hundred degrees Celsius, black bodies start to emit visible wavelengths ending up beyond visible into ultraviolet and beyond
Every object emits blackbody radiation although you do not normally notice it because our eyes are only sensitive to a very small portion of the electromagnetic spectrum.  An object must be quite hot for it to emit visible light.

10. Blackbody radiation curves
For increasing temperatures, the sequence of radiated colors is: black, red, orange, yellow-white, bluish-white
Black body radiation provides us with a set of very precise working equations that relate the temperature of an object to the light it emits

11. The higher the temperature of a black body, the more energy is emitted in each band of wavelengths and black body becomes "brighter".
The radiation emitted at the highest intensity, represented by the peak of the spectrum, doesn't fall in the visible region unless the temperature is very high, over 3700K.

12. Color Temperature
As color temperature rises, so the light emitted shifts towards bluer hues.
In practice, the actual temperature is not the same as the color temperature, but is a reasonable approximation in many cases [correction factors can be used]
Energy given off by an object solely by virtue of its temperature is called Thermal or Black Body Radiation

13. Color temperature

14. So? Blackbodies and astronomy
Our Sun is an another example of a "real" blackbody radiator.
It's spectrum isn't as smooth as the "ideal" ( it is pitted and bumpy due to real-world conditions including, but not limited to, absorption of the radiation en route to the earth) but it is close enough.  
It fact, measuring color is the primary means astronomers have of determining the temperatures of distant stars.

15. Light emitted by the Sun
Wavelength of Peak emission = 2898 microns / Temperature of Blackbody (Kelvin).

16. Temperature
All objects emit electromagnetic radiation, and the amount of radiation emitted at each wavelength determines the temperature of the object
Hot objects emit more of their light at short wavelengths, and cold objects emit more of their light at long wavelengths
The radiation temperature of an object is related to the wavelength at which the object gives out the most light.
The amount of light emitted at a particular wavelength = intensity
Plot the intensity of light from an object at each wavelength = blackbody curve

17. Temperature
Stars hotter than the sun (over 6,000 degrees C) put out most of their light in the blue and ultraviolet regions of the spectrum.
Stars cooler than the Sun (below degrees C) put out most of their light in the red and infrared regions of the spectrum.
Solid objects heated to degrees C appear red but are putting out far more (invisible) infrared light than red light.

18. Electromagnetic spectrum
Gamma
X-rays
Ultraviolet
Visible
Infared
Radio
Range of different wavelengths

19. Electromagnetic spectrum

21. Gamma rays Shortest wavelength <0.01 nanometers (size nucleus)
Highest frequency and most energetic
Nuclear reactions, exploding stars, black holes

22. X-rays Wavelength 0.01 to 10 nanometers (size of atom)
Cam be generated from exploding stars

23. Ultraviolet Wavelength: 10 to 310 nanometers (size of virus)
Produced by young, hot stars

24. Visible
Wavelength: 400 to 700 nanometers (size of molecule to protozoan)
Most of Sun’s emission
Only portion detected by our eyes– biologically active region of spectrum

25. Infared
Wavelength: 710 nanometers to 1 millimeter (pin point to small plant seeds)

26. Radio waves Wavelength: over 1 millimeter Lowest energy, longest waves
Found everywhere: background radiation of universe, interstellar clouds, remains of supernovas

27. Use Microwave oven to demonstrate speed of light and wavelength
Marshmallow worksheet
Chocolate bar and microwaves
Marshmallows and Microwaves

28. Sun as source of electromagnetic Radiation
The Sun is the Earth's primary source of electromagnetic radiation
It takes about 8 minutes for electromagnetic radiation emitted from the Sun to reach the Earth.
The major fraction of the Sun's radiation is in the "visible" part of the electromagnetic spectrum, however the Sun radiates electromagnetic energy over a very wide range of wavelengths.

29. Radiation from the Sun . Visible
                                         
Radiation from the Sun
Visible
“White" light that illuminates the Earth's surface
Actually a continuous blend of colors UV
High energy component
Sun's short wavelength ultraviolet radiation is filtered by Earth's ozone layer
Infared
Thermal radiation
Water vapor in atmosphere blocks most of the Sun's incoming infrared radiation
Radio waves
Sun at 330MHz (wavelength about 1m)
X-rays
Bright spots on this image are regions of intense X-ray emission

30. Sun’s radiation
At Earth's distance from the Sun, about 1,368 watts/m2 of energy in the form of EM radiation from the Sun fall on an area of one square meter
AKA solar constant

31. Radiation reaching the earth’s surface
Various wavelengths of solar EM radiation penetrate Earth's atmosphere to various depths. All of the high energy X-rays and most UV is filtered out before it reaches the ground. Much of the infrared radiation is also absorbed by our atmosphere. Most radio waves do make it to the ground, along with a narrow "window" of IR, UV, and visible light frequencies.

32. Albedo Degree to which a surface reflects light that strikes it.
An extremely reflective surface that doesn't absorb any of the light = an albedo of 1, while a surface that reflects none of the light that hits it = an albedo of 0.
Albedo affects ability of planet to absorb sunlight, thus converting it to heat that can warm the planet and drive its climate.
Earth's overall average albedo is about 0.31.
Without clouds our planet's albedo would be around 0.15, so clouds roughly double Earth's albedo.

33. Insolation solar radiation is received at the Earth's surface

34. Earth’s energy balance
Green-house effect
FAQ 1.1, Figure 1. Estimate of the Earth’s annual and global mean energy balance. Over the long term, the amount of incoming solar radiation absorbed by the Earth and atmosphere is balanced by the Earth and atmosphere releasing the same amount of outgoing longwave radiation. About half of the incoming solar radiation is absorbed by the Earth’s surface. This energy is transferred to the atmosphere by warming the air in contact with the surface (thermals), by evapotranspiration and by longwave radiation that is absorbed by clouds and greenhouse gases. The atmosphere in turn radiates longwave energy back to Earth as well as out to space. Source: Kiehl and Trenberth (1997). 34

35. Ionizing radiation
Ejection of electrons from an atom or molecule resulting in formation of a positive ion
Ionizing means there is sufficient energy to eject electrons
X-rays and gamma rays and nuclear radiation
Threshold of ionization is UV range
Radioactivity refers to the particles emitted as a result of nuclear instability
Common types:
Alpha
Beta
Gamma

36. Ionizing radiation Gamma rays = EM rays that come from nucleus
Alpha rays = two protons and two neutrons
Beta particles = high energy electrons released from decaying nucleus
Cosmic rays, alpha and beta particles are referred to as particle radiation
Gamma is not a particle

37. Non-ionizing radiation
Radiation that is disruptive to an atom and makes it a chemically active ion
EM radiation in the visible or longer wavelength range does not have sufficient quantum energy to ionize an atom--- therefore NON-ionizing radiation
Threshold for ionization is in UV range
Effects of of non-ionizing radiation:
Photosynthesis
Infared warming of the Earth
Heating in general (microwave ovens)
Power transmission, communication, vision

38. Why Does the Sun Look Yellow?
Sunlight in space is a combination of every wavelength of electromagnetic radiation (EMR), including those wavelengths that human vision cannot sense and the Earth's atmosphere absorbs at high altitude.
Humans perceive various combinations of full spectrum wavelengths as white. Sunlight is very "white“.
The Sun visible radiation peaks in the yellow-green visible spectrum.
Yellow-green is the color that humans have the knack of sensing most intensely– so we see YELLOW SUN
The very hottest stars, such as Sirius, emit radiation that peaks in the blue spectrum, but our star is not that hot.

39. Why is Sky Blue?
The blue color of the sky is due to light scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.
However, much of the shorter wavelength light is absorbed by the gas molecules.
The absorbed blue light is then radiated in different directions. It gets scattered all around the sky.
Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

40. Sky blue
As you look closer to the horizon, the sky appears much paler in color because to reach you, the scattered blue light must pass through more air.
Some of it gets scattered away again in other directions.
Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.

41. Resources Mystery of light MIT http://mitworld.mit.edu/video/291
Electricity and magnetism
National Radio Astronomy Observatory
adiowaves#blackbody