1. Light

2. What is light?
Early scientists thought it was made up of particles (protons, neutrons and electrons)
Travels in a straight line instead of spreading out (like a wave would)
Later scientists discovered light does spread so they thought it was a wave
Einstein published his photoelectric effect which says that light is made up of particles that have wavelike tendencies

3. Photons and light
The particles that light is made up of are known as photons
Massless bundles of energy
The energy comes from accelerating electrons that are typically found in atoms
The energy is partially electric and partially magnetic
Hence the term: electromagnetic waves

5. The speed of light
Have you ever been to a baseball game where you see the bat hit the ball, but hear it a second later?
That is because light travels about 100,000 times faster than sound!!!
Light travels at approximately 300,000,000 m/s (300,000 km/s) in a vacuum
It only takes light from the sun 8 minutes to reach the Earth, which is 93 million miles away!!

6. The Speed of Light
Discuss with your neighbor what you think happens to the speed of light as it travels through our atmosphere or through water
Light travels slightly slower through the atmosphere and 25% slower when it travels through water

7. The Electromagnetic
Spectrum

8. What is the electromagnetic spectrum?
The range of all electromagnetic waves
All EM waves travel at the same speed (300,000,000 m/s = speed of light), but have different wavelengths

9. What is the electromagnetic spectrum?
How is that possible? Discuss with a neighbor (hint: think about the wave speed formula)
They have different frequencies!
As you move from left
to right on the spectrum,
frequency increases

10. Radio Waves Any EM wave with a wavelength that is longer than 30 cm
The longest wavelength of all EM waves
What does that tell you about the frequency?
They have low frequencies

11. Radio broadcasting
Different radio stations are created through modulation
Changing either the amplitude or the frequency of the wave
AM radio = amplitude modulation
Travel further distances
FM radio = frequency modulation
Shorter distances, but clearer
sound due to less interference

12. Microwaves – not just for cooking
Shorter wavelengths and higher frequencies than radio waves
Wavelength is between 1mm and 30 cm
Cell phone signals are carried on microwaves

13. Microwaves – not just for cooking
Any signal sent between the earth and satellites in space are microwaves
Also used in radar guns
Reflected microwaves are used to calculate the speed of passing cars

14. Infrared Waves
Shorter wavelengths and higher frequencies than microwaves
Between 700 nm and 1 mm
Most things give off infrared waves
The amount given off depends on temperature of the object
Warmer object give off more than cooler objects
You can’t see IR waves with the naked eye
Night vision glasses let you see IR waves

15. Visible Light
A very small part of the EM spectrum that can be seen by humans
Shorter wavelengths and higher frequencies than IR waves
Wavelengths between 400 and 700 nm
Only some of the light from the sun is visible light
In other words, we can not see all of the light emitted from the sun
We see white light from the sun
A combination of all of the colors of light

16. Colors of light
Different wavelengths of visible light are seen as different colors
Longest wavelength = red
Shortest wavelength = violet
Roy G Biv – visible spectrum
Red
Orange
Yellow
Green
Blue
Indigo
violet

18. Ultraviolet Light Also produced by the sun
Shorter wavelengths and higher frequencies than visible light
Wavelengths between 60 and 400 nm

19. Ultraviolet Light The good side: The bad side:
Used to kill bacteria on food and tools
Small amounts help your skin to produce vitamin D
The bad side:
Causes sunburn, skin cancer, wrinkles and eye damage
Most UV rays from the sun do not reach the Earth

20. X-rays Some of the shortest wavelengths
Wavelengths between .1 and 60 nm
Can pass through materials because they are so short
Too much exposure to them can be harmful to human cells

21. Gamma rays Wavelengths shorter than 0.1 nm
Used to treat some forms of cancer
May kill some healthy cells along with the cancer cells
Used to kill bacteria in food