1. A light review: Our primary source of light is the sun.
Light travels in straight lines at a speed of 3.00 x 108 m/s.
Light energy from the sun travels through space , reaches earth, and some of it turns to heat energy and warms the earth’s air.
Light from the sun also travels to the cells of green plants (producers) and is stored as energy. The peak wavelength of our sun is green.
When light reaches an object, it is absorbed/ reflected (giving it colour), or passes through it.

2. EM Theory
Henry and Faraday linked electricity and magnetism by finding that changing magnetic fields will generate a current in nearby conductors.
The linking of these two forces (electric and magnetic) allowed physicists to move closer to the ultimate goal of linking all the forces into a Grand Unified Theory (G.U.T.)
The nuclear forces (weak and strong) are explained by an interaction of EM waves
Gravity is the elusive force that has not been nailed down into the G.U.T.

3. EM Theory
In 1846, Faraday theorized that light could be a vibration of electric and magnetic fields (dropping the ether model)
James Maxwell proved Faraday’s theory mathematically, 10 years later.
All electromagnetic waves are generated by accelerated charges.
As a charge is accelerated, it will continually emit excess energy as an EM wave (to limit the particle’s velocity to less than “c”).
The accelerated charge generates a changing magnetic field which creates a changing electric field, which generates a changing magnetic field, etc

4. EM Theory

5. What is light really? Electromagnetic radiation waves
Light waves are three dimensional
Light waves vibrate in all planes around a center line.
The waves have high points called “crests.”
Waves also have low points called “troughs.”
*The distance from one crest to the next crest is called a “wavelength.”
*The number of waves passing a given point in one second is called the “frequency.”
wavelength

6. *Electromagnetic Radiation
Electromagnetic radiation can be described in terms of a stream of photons. Each photon is traveling in a wave-like pattern, moving at the speed of light and carrying some amount of energy.
The only difference amongst radio waves, visible light, and gamma-rays is the amount of energy of the photons. Radio and AC waves have photons with low energies. Microwaves have a little more energy than radio waves. Infrared has still more energy.
As we move down the chart we see visible, ultraviolet, X-rays, and gamma-rays whose photon energies gradually increase.
Gamma and Cosmic rays have the highest energy waves.

7. Remember radio waves are long…and gamma rays are small.
Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic

8. EM Theory
An electron forced to oscillate at MHz will produce an FM radio wave
An electron accelerated by a Mega-Volt and fired into a metal target will produce X-rays (rapid deceleration of electrons)
A magnetron in a microwave oven accelerates charges to produce an EM wave that is forced to oscillate at about 2.4 x 109 Hz (the electric field spins polar water molecules to create heat).

9. Radio (Longest electromagnetic waves)
Emitted by
Astronomical Objects
Radio Station Transmitters
Detected by
Ground based radio telescopes
*If you turn on a radio,, it will convert the radio wave energy into sound energy.

10. Television
Shorter than radio, also used to carry messages (pictures & sound) to our TV sets.
We can detect the TV waves around us with our televisions.

11. Microwave Emitted by: Detected by Gas clouds collapsing into stars
Microwave Ovens
Radar Stations
Cell Phones
Detected by
Microwave Telescopes
Food (heated)
Cell phones
Radar (systems)

12. Infrared (Heat or Thermal) Are you a source of infrared? YES you are!
Emitted by
Sun and stars (Near)
TV Remote Controls
Food Warming Lights (Thermal)
*Everything at room temperature or above,=HEAT
Detected by
Infrared Cameras
TVs, VCRs,
Your skin

13. Visible Each color is a different size wave
Visible Each color is a different size wave. Red the longest & violet the shortest
Emitted by
The sun and other astronomical objects
Laser pointers
Light bulbs
Detected by
Cameras
(film or digital)
Human eyes
Plants (red light)
Telescopes
RoyG.Biv

14. Ultraviolet Sunburn / black light
He can get skin cancer!
Emitted by
Tanning booths (A)
The sun (A)
Black light bulbs (B)
UV lamps
Detected by
Space based UV detectors
UV Cameras
Flying insects (flies)

15. X-ray Emitted by Detected by Astronomical objects X-ray machines
CAT scan machines
Older televisions
Radioactive minerals
Airport luggage scanners
Detected by
Space based X-ray detectors
X-ray film
CCD detectors

16. Chandra X-ray Observatory
Chandra is designed to observe X-rays from high energy regions of the universe, such as the remnants of exploded stars.
The most sophisticated observatory built to date.
Deployed by the Space Shuttle Columbia on July 23, 1999,
Chandra X-ray Observatory
*Slide from 2004 NSTA Conference

17. Gamma Ray (Short electromagnetic waves but more energetic)
Emitted by
Radioactive materials
Exploding nuclear weapons
Gamma-ray bursts
Solar flares
Detected by
--Geiger counters
Gamma detectors and astronomical satellites
Medical imaging detectors

18. Sources of g-ray Emission
• Black holes
• Active Galaxies
• Pulsars
• Diffuse emission
• Supernovae
Gamma-ray bursts
• Unidentified

19. COSMIC Rays (The highest energy waves and the deadliest)
Cosmic rays come from deep space and can pass through the Earth.
Neutrinos are emitted by all stars
Dark matter/energy?

20. How big are the waves? A great question! Radio waves= (Buildings to
human size);
Microwaves
(Humans-beetles);
Infrared waves
(Eye of a needle);
Visible waves
(microscopic size)!
All the rest are the size of molecules, atoms, atomic nuclei and smaller..

22. EM Waves
In 1865, Maxwell proved that all EMR travels at the speed of light where:
The permittivity of free space is
εo = 8.85x10-12 C2/(N●m2) and the
permeability of free space is
μo = 4π x 10-7 T●m/A
The speed of light is defined today as c = m/s

23. EM Waves EM waves are produced using the following steps:
Energy is supplied to a source of EM radiation
The source does work on charges making them accelerate
The charges continually emit EMR radiating away excess kinetic energy
The atomic model proved a challenge as accelerated electrons (in the Bohr-orbit model) did not radiate EMR continuously (the atom would collapse) and Bohr solved this by stating this didn’t occur in the atom.